minerales (1)

Biotite K2(Mg,Fe)2(OH)2(AlSi3O10)

Optical Properties:

Biaxial negative; strong pleochroism in brown, reddish brown, and green; extinction is parallel to one excellent cleavage. Near extinction, a "crinkly", or sparkly appearance is common (upper left photo). The most distinctive properties of biotite are the combination of strong pleochroism and parallel extinction. The view upper right, in plane polarized light, shows a biotite flake lying on its cleavage, with tiny inclusions of zircon; radioactive decay of uranium in the zircon crystals has destroyed the biotite lattice near the inclusions, creating dark a dark halo around each zircon.

Although hornblende has similar pleochroic colors and can be confused with biotite, hornblende has inclined extinction, not parallel extinction.

Occurrence:

Biotite is a common mineral in siliceous intrusive rocks such as granite, quartz monzonite, granodiorite, and tonalite. It is less common in siliceous volcanic rocks. Biotite appears in shale, phyllite, and schist derived from shale protoliths.Alteration:

In the photo above, biotite (dark mineal) is altering to chlorite.

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INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/intrus/a_29.gif" \* MERGEFORMATINET Clinopyroxene

Optical Properties:

The clinopyroxene group includes diopside, augite, jadeite, pigeonite, hedenbergite, and others. It is generally difficult to distinguish between individuals in this group optically. All are biaxially positive, with moderate relief and up to second order birefringence colors, and all have pyroxene 87 degree cleavage and inclined extinction. Many clinopyroxenes have pale greenish pleochroism.

The photos above show a clinopyroxene grain in crossed (left) and uncrossed polarizers; exsolution lamellae of orthopyroxene are clearly visible in the left photo.

Occurrence:

Clinopyroxenes are abundant in many intrusive and extrusive igneous rocks, including diorite, gabbro, the peridotite family, basalt, and andesite. They also occur in metamorphosed mafic rocks, and jadeite is a constituent of some blueschist facies rocks.

INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/mineral/m_5.gif" \* MERGEFORMATINET

Above: clinopyroxene crystal in basalt: crossed polarizers on left, plane light on right. Field of view 1.5 mm.

INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/mineral/m_3.gif" \* MERGEFORMATINET Complex twins in lunar mare clinopyroxene in crossed polarizers (left). Two cleavages in pyroxene in plane polarized light (right).


INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/intrus/a_20.gif" \* MERGEFORMATINET Hornblende Ca2(Mg,Fe,Al)5(OH)2[(Si,Al)4O11]2

Optical Properties:

Biaxial negative; high 2V (50-85 degrees); strong pleochroism in greens and browns; 2 cleavages at 56 degrees; moderate birefringence (second order colors, often masked by the mineral's strong color. Hornblende's strong pleochroism and inclined extinction are its most distinctive characteristics.

Occurrence:

Hornblende is common in many intrusive igneous rocks ranging from granite to gabbro; it is also present in medium grade metamorphosed mafic rocks. Hornblende occurs in some volcanic rocks, but it is less abundant in extrusive rocks than in intrusive rocks.

Alteration:

Hornblende commonly alters to biotite or chlorite.

The photographs above show hornblende in crossed polars (left) and in plane polarized light (right photo). The black grains are an opaque mineral (magnetite). The dark reddish brown mineral in the left photo is biotite.


The photos above (left in plane light, right under crossed polarizers) show dark hornblende in the upper left corner, and dark biotite in the lower right, with plagioclase in a diorite.


INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/mineral/m_32.gif" \* MERGEFORMATINET Leucite KAl(SiO3)2

Optical Properties:

Pseudoisometric; colorless; euhedral crystals; very weak birefringence; polysynthetic twins in several directions.The photos above show leucite under crossed polarizers (left view; note polysynthetic twins), and plane polarized light (right photo).

Occurrence:

Restricted to silica undersaturated lavas and tuffs, almost exclusively as phenocrysts.


INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/mineral/m_10.gif" \* MERGEFORMATINET Microcline KAlSi3O8

Optical Properties:

Biaxial negative; first order gray interference color; "basketweave" twinning (multiple twins crossing at almost right angles), as shown in the pictures above, is almost always present; note how twins pinch and swell, unlike most plagioclase twins. In the photo on the right microcline occurs with biotite and quartz.

Occurrence:

Common in quartz-rich intrusive rocks such as granite, and in some moderate to high temperature metamorphic rocks; it does not occur in volcanic rocks. It may be intergrown with plagioclase to form perthite. At higher temperature, orthoclase forms instead of microcline.


INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/intrus/a_18.gif" \* MERGEFORMATINET Muscovite KAl2(OH)2(AlSi3O10)

Optical Properties:

Biaxial negative, small 2V (30-40 degrees); clear in plane polarized light; high birefringence, producing up to third order colors; 1 excellent cleavage; parallel extinction. Muscovite is a distinctive mineral, because of its high birefringence, parallel extinction, and excellent basal cleavage.

The two photographs above show muscovite in crossed polarizers (left photo) and uncrossed polarizers (right photo) in granite. In the left picture, muscovite shows yellow to blue interference colors; it is colorless and clear in uncrossed polarizers. Microcline is in the lower right and at the right edges of the photographs, and biotite is the pleochroic (colored) mineral most clearly visible in the right photo.

In the left photo below (crossed polarizers), a muscovite grain shows high birefringence and bent cleavage planes. In the plane polarized light view on the right, clear, subhedral muscovite cuts diagonally across the picture and appears to penetrate the dark biotite grain.

INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/mineral/m_34.gif" \* MERGEFORMATINET Occurrence:

Common in pegmatites, low to medium grade metamorphic rocks, and present in some granites.


Myrmekite

Optical Description:

Myrmekite is a "wormy" intergrowth of quartz in sodic plagioclase. In the photo above, quartz is the light gray "worms" in a plagioclase grain that is extinct. Other minerals present are plagioclase (upper right) , biotite (upper left), and quartz (extinct grain in lower left corner.

Occurrence:

Myrmekite occurs in quartz-rich intrusive rocks.


Nepheline (Na,K)(Al,Si)2O4

Optical Properties:

Uniaxial -; colorless; poor cleavage; low relief; first order gray interference colors; parallel extinction.

In the photo above (crossed polarizers), nepheline poikilitically encloses twinned plagioclase crystals.

Occurrence:

Silica undersaturated igneous rocks, such as nepheline syenite, phonolite, and some basalts. Does not occur with quartz.


INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/ultra/b_40.gif" \* MERGEFORMATINET Olivine (Mg,Fe)2SiO4

Optical Properties:

Biaxial + or -; very high 2V. Usually colorless in plane light, but Fe-rich varieties have green pleochroism; poor cleavage in one direction; parallel extinction; up to third order interference colors. Commonly has conchoidal fractures and some alteration to serpentine or talc. Distinguished from orthopyroxene by high birefringence, and from clinopyroxene by parallel extinction.

The photos above (crossed polarizers on left, plane light view on right) show the usual appearance of olivine in ultramafic rocks: curved fractures, andhedral grains, high relief, high birefringence.

Occurrence:

Olivine is abundant in most ultramafic rocks and is a common constituent of many basalts and gabbros. It is less abundant in diorites and andesites.

The photos below are a dunite on the left (>90% olivine), showing the mineral's high birefringence; on the right is a mixture of olivine and twinned plagioclase, showing the difference in interference colors of the two minerals.

INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/ultra/b_44.gif" \* MERGEFORMATINET More OlivinePetrography Home Minerals List Rocks List

Orthoclase KAlSi3O8

Optical Properties:

Biaxial negative; first order gray interference colors; negative relief; simple twins only: no polysynthetic twins. Commonly has a cloudy appearance, like the light gray grain in the photo above, because of clay alteration. Distinguished from quartz by biaxial optics, twins, and negative relief.

Occurrence:

Common in some siliceous intrusive rocks, syenite, trachyte, and high temperature metamorphic rocks.


Orthopyroxene (Mg,Fe)SiO3

Optical Properties:

Enstatite, hypersthene, and ferrosilite are members of the orthopyroxene solid solution series. All have low birefringence (first order red maximum), parallel extinction, and pyroxene 87 degree cleavage. Pale green, pale red, or pale purple pleochroism occurs in some grains. Distinguished from clinopyroxene by low order interference colors and parallel extinction. The photo above shows one cleavage and thin exsolution lamellae.

Occurrence:

Orthopyroxene occurs with clinopyroxene in many igneous rocks, such as gabbro, diorite, basalt, andesite, and the peridotite family. It is an indicator mineral for the granulite and pyroxene hornfels facies of metamorphism.

Fine exsolution lamellae in orthopyroxene. Field of view 1.5 mm, crossed polarizers.


Oxyhornblende (Lamprobolite, Basaltic Hornblende)

Ca,Mg,Fe,Al silicate, an amphibole

Optical Properties:

Biaxial -; 2V 60-80 degrees; yellow to reddish brown pleochroism; amphibole cleavage; extinction angle close to 0 degrees. Pleochroic colors are distinctive.

The photograph above shows phenocrysts of lamprobolite in andesite.

Occurrence:

Volcanic rocks such as andesite and others.


Perthite KAlSi3O8 and Plagioclase (Na-Ca Al Silicate)

Optical Properties:

Perthite is actually two minerals: an intergrowth of sodic plagioclase in K-feldspar (orthoclase or microcline). The intergrowths are commonly stringy (as in the photo above), but they may be globular, lensoid, or other shapes. First order gray interference colors. When the optic sign is determined, it may be either + or -, depending on whether the lens is focused on K-feldspar or intergrown plagioclase.

Occurrence:

Common in siliceous intrusive rockssuch as granite and quartz monzonite; also in syenite, trachyte, and some metamorphic rocks.


INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/intrus/a_6.gif" \* MERGEFORMATINET

INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/mineral/m_8.gif" \* MERGEFORMATINET Plagioclase NaAlSi3O8 to CaAl2Si2O8

Optical Properties:

Biaxial + or -, first order gray to very pale straw yellow interference colors; low relief; polysynthetic twinning is very common, as in the photos on the left, which helps distsinguish plagioclase from orthoclase; twins are typically continuous, with parallel sides, unlike microcline. Plagioclase also may be strongly zoned, as in the photos at the right above: normal zoning when the center of the grain is more Ca-rich than the edges, and oscillatory zoning when the composition alternates from Ca- to Na-richer zones.

Plagioclase composition may be determined by several optical techniques. Perhaps the easiest technique to apply is the Michel-Levy method.

Occurrence:

Plagioclase is the most abundant mineral in Earth's crust, occurring in most igneous and metamorphic rocks.

Sericite (fine-grained muscovite) flakes altering plagioclase grain in the center of the picture; zoned plagioclase in the lower left; twinned plagioclase upper right.


INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/mineral/m_7.gif" \* MERGEFORMATINET Quartz:

Optical properties:

Uniaxial positive; first order interference colors (gray to pale yellow); undulant extinction; clear in plane polarized light; conchoidal fracture; no visible cleavage or twinning. In intrusive rocks, quartz is typically a late-forming mineral and therefore interstitial to other minerals.

The photos on this page are under crossed polarizers: on the left above is strained quartz in a granite; on the right is a quartz phenocryst in rhyolitic glass, showing conchoidal fracture. The photos below show quartz grains in a sedimentary rock, conglomerate. On the left, Boehm lamellae in the grains indicate a high stress regime; the grains on the right show sutured grain boundaries and internal strain, indicating a probable metamorphic origin.

Occurrence:

Many intrusive rocks, such as granite, quartz monzonite, granodiorite, tonalite, etc; extrusive rocks such as rhyolite, dacite, etc., and many metamorphic and sedimentary rocks.

INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/sedim/s_69.gif" \* MERGEFORMATINET Petrography Home Minerals List Rocks List

INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/extrus/c_50.gif" \* MERGEFORMATINET Sanidine KAlSi3O8

Optical Properties:

Biaxial negative, small 2V, first order gray interference color, simple twins, 2 cleavages. Both photos above are under crossed polarizers; on the left is a sanidine grain with Carlsbad twin; on the right, the large grain at the right is sanidine; the phenocrysts at the left edge of the photo are quartz. The rocks in both cases are rhyolites.

Occurrence:

Restricted to volcanic rocks or very high temperature contact metamorphic rocks (sanidinite facies) that are rich in potassium.


INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/mineral/m_50.gif" \* MERGEFORMATINET Sphene (Titanite) CaTiSiO5

Optical Properties:

Biaxial +; 2V 23-50 degrees; colorless to very pale yellow to brown or green pleochroism; extreme birefringence; very high relief.

The photos above, both in plane polarized light, show the very high relief of nearly colorless sphene in a feldspar-rich rock. The pleochroic mineral in the picture on the right is acmite.


INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/mineral/m_28.gif" \* MERGEFORMATINET Zeolites

The zeolite group of minerals are hydrous Ca-Na aluminum silicates. Only four of the group are listed here; there are many more varieties, and many look similar in thin section. The zeolites are listed here as secondary minerals in igneous rocks, a common environment for them, but they are widespread in some marine and fresh water deposits as well.

Analcite NaAl(SiO3)2.H2O

Isometric, therefore extinct under crossed polarizers. Occurs as vesicle fillings and replacement in some lavas, and deposited in some lake beds. Shown as vesicle filling upper left (crossed polarizers).

Heulandite H4CaAl2(SiO3)6.3H2O

Biaxial +; first order gray interference colors; 2V 0-48 degrees; parallel extinction; 1 excellent cleavage. Occurs as a secondary mineral in volcanic rocks. Shown as vesicle filling in upper right photo.

INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/mineral/m_26.gif" \* MERGEFORMATINET Thomsonite NaCa2Al5(SiO4)5.6H2O

Biaxial +; colorless in plane polarized light; low birefringence; fibrous to bladed or columnar aggregates. Occurs as cavity filling in igneous rocks, as shown under crossed polarizers at upper left.

Stilbite H4(Ca,Na2)Al2(SiO3)6.4H2O

Biaxial-; first order gray birefringence; colorless in plane polarized light; 1 good direction of cleavage; wavy extinction. Occurs as cavity fillings in igneous rocks and as hydrothermal alteration.


Andalusite Al2SiO5

Optical Properties:

Biaxial -; very high 2V; usually colorless, may be red under crossed polarizers; first order gray interference colors; typically euhedral (idioblastic) crystals; 2 cleavages; parallel or symmetrical extinction. Carbonaceous inclusions may be arranged symmetrically to form a variety called chiastolite.

The photograph shows a porphyroblast of andalusite, with faint dark cross of carbonaceous specks, in a fine-grained hornfels.

Occurrence:

Common mineral in contact metamorphosed shales; also occurs in regional, high temperature, low pressure metamorphic rocks and in granite pegmatites.


INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/mineral/m_62.gif" \* MERGEFORMATINET Chlorite Mg,Al silicate family of micaceous minerals

Optical Properties:

Biaxial; depending on the composition and chlorite variety, chlorite may be positive or negative; 2V 0-30 degrees; colorless to pale green pleochroism; low birefringence (first order colors, though occasionally anomalous blue); typically occurs as tiny flakes.

The photos above show chlorite filling a vesicle in basalt. Plane polarized light on the left, crossed polarizers on the right.

Occurrence:

Chlorite is a common alteration of ferromagnesian minerals; it is abundant in many low grade metamorphic rocks.


INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/mineral/m_22.gif" \* MERGEFORMATINET Epidote-Clinozoisite Ca2(Al,Fe)3(OH)(SiO4)3

Optical Properties:

Biaxial + or -; 2V 56 to 89 degrees; colorless (clinozoisite) to yellowish green (epidote) pleochroism (upper right photo); birefringence weak in clinozoisite, to strong in epidote; clinozoisite typically has anomalous blue interference color (upper left photo); extinction is parallel in elongate grains.

Occurrence:

Commonly occurs in low to medium grade metamorphic rocks, and as hydrothermal or deuteric alteration in igneous rocks.


INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/mineral/m_14.gif" \* MERGEFORMATINET Garnet Mg,Fe,Mn,Ca,Cr silicates

Optical Properties:

Garnet is isotropic, therefore extinct under crossed polarizers. In thin section, it may be colorless, pale red to dark brown, greenish, etc. All members of the garnet family have very high relief, and they commonly form euhedral crystals.

The photograph above left shows garnet under uncrossed polarizers; chlorite is altering the garnet along its left margin and within a fracture. The photo on the right with crossed polarizers shows a garnet crystal at extinction, surrounded by muscovite and glaucophane in glaucophane schist.

Occurrence:

Garnet is characteristic of metamorphic rocks such as schists, but it may also be found less commonly in igneous rocks.

In the photograph below, under crossed polarizers, an extinct garnet grain in a schist contains numerous quartz inclusions.


INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/mineral/m_13.gif" \* MERGEFORMATINET Glaucophane Na2Mg3Al2(OH)2(Si4O11)2

Optical Properties:

Biaxial -; strong pleochroism, blue to violet to colorless to pale brown; amphibole cleavage.

The two photos above are in plane polarized light, illustrating the unique pleochroism of glaucophane.

Occurrence:

Occurs in low grade metamorphic rocks, associated with white mica, albite, quartz, chlorite, epidote, and occasionally lawsonite and jadeite.


The picture on the left, in plane polarized light, is a mixture of lightly colored glaucophane, colorless white mica, and dark, high relief epidote in a low grade schist. On the right is a crossed polarizers view of a glaucophane schist with a large, isotropic garnet in the center, surrounded by highly birefringent glaucophane and white mica.


INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/mineral/m_45.gif" \* MERGEFORMATINET Kyanite Al2SiO5

Optical Properties:

Biaxial -; very high 2V; colorless to pale blue in plane polarized light; tabular crystals; 2 cleavages; high relief; maximum first order red interference colors; inclined extinction that can almost be parallel.

The photos above and below show kyanite in crossed polarized view on the left, and in plane polarized light on the right. Kyanite is surrounded by biotite and muscovite in the top photos, and by quartz in the lower photos. The cleavage, relief, and bladed form of kyanite are clearly visible.

INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/meta/dynamo/b_109.gif" \* MERGEFORMATINET Petrography Home Minerals List Rocks List

INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/mineral/m_17.gif" \* MERGEFORMATINET Lawsonite H4CaAl2Si2O10

Optical Properties:

Biaxial +; 2V>80 degrees; colorless; interference colors to second order; polysynthetic twinning is apparent is some grains; two good cleavages. Both of the photos above are under crossed polarizers. In the photo on the left, polysynthetic twins are apparent; on the right, various interference colors of lawsonite are shown.

Occurrence:

Lawsonite is an indicator mineral of blueschist grade metamorphism (high pressure, low temperature metamorphism). It is associated with white mica, glaucophane, epidote, chlorite, albite, quartz, and occasionally jadeite and aragonite.


INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/meta/burial/a_86.gif" \* MERGEFORMATINET Prehnite H2Ca2Al2(SiO4)3

Optical Properties:

Biaxial +; variable 2V; moderate birefringence, up to high second order colors;colorless in plane polarized light; 1 good cleavage; high relief; parallel extinction; tabular crystals.

The photos above illustrate typical prehnite occurrences, in veins in low grade metamorphic rocks. On the left, in plane polarized light, is a thin vein with pumpellyite and clear, elongate crystals of prehnite. On the right, under crossed polarizers, prehnite birefringence is displayed. Both photographs have a field of view of 1.5 mm.

Occurrence:

Occurs in the matrix and in veins in low temperature metamorphic rocks, and as a vesicle filling in some lavas.


INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/meta/burial/a_88.gif" \* MERGEFORMATINET Pumpellyite Ca4(Mg,Fe,Mn)(Al,Fe,Ti)5O(OH)3[Si2O7]2[SiO4]2.H2O

Optical Properties:

Biaxial -; 2V varies from low to very high; moderate interference colors, which may be anomalous; colorless to green, brown, or yellow in plane polarized light; generally in fibrous form. Crossed polarizer (left, above) and plane polarized light views (right, above) show the typical appearance of pumpellyite in thin section.

The photo below (plane polarized light) shows pumpellyite in a thin vein, a typical occurrence in blueschist metamorphic veins.

Occurrence:

Pumpellyite is a low temperature metamorphic mineral that commonly occurs with chlorite, albite, prehnite, clinozoisite, etc.


INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/ultra/b_43.gif" \* MERGEFORMATINET

Serpentine H4Mg3Si2O9

Optical Properties:

Serpentine minerals may be either biaxial + or -, with 2V varying from 0 to 90 degrees. All members of the group have low birefringence (first order yellow maximum) and parallel extinction. The mineral habit is fibrous, and in plane polarized light grains are colorless to pale green. Grain size is typically too small to determine many optical properties.

Occurrence:

The serpentine group of minerals is formed by metamorphism and hydrothermal alteration of mafic minerals, such as olivine and pyroxene.

The photos above show serpentine in crossed polarizers (left) and plane polarized light (right). The rock shown is almost 100% serpentine; the equant crystal forms seen are serpentine pseudomorphs after olivine.

The picture below left (1.5 mm field of view, crossed polarizers) shows light gray stringers of serpentine altering clinopyroxene (at extinction). On the right is a clinopyroxene grain surrounded by gray serpentine (crossed polarizers).

INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/mineral/m_25.gif" \* MERGEFORMATINET Petrography Home Minerals List Rocks List

INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/meta/dynamo/b_111.gif" \* MERGEFORMATINET Sillimanite Al2SiO5

Optical Properties:

Biaxial +; small 2V (20-30 degrees); slender, needle-like habit; high relief; up to middle second order interference colors; parallel extinction.

The photos above show the needle-like form and birefringence of sillimanite (crossed polarizers on left, plane light on right).

The lower pictures (of two different sillimanite schists) show somewhat finer- grained needles of sillimanite (crossed polarizers on left, plane light on right).

INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/mineral/m_47.gif" \* MERGEFORMATINET Occurrence:

Occurs principally in medium to high grade regional and contact metamorphosed shales.


INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/meta/dynamo/b_107.gif" \* MERGEFORMATINET Staurolite 2Al2SiO5.Fe(OH)2

Optical Properties:

Biaxial +; very high 2V; colorless to yellow to yellow-brown pleochroism; high relief; maximum interference color first order red; parallel or symmetrical extinction; prismatic crystals. Distinguishing features are color and pleochroism, and the typical presence of numerous quartz inclusions.

The photos above (crossed polarizers on left, plane polarized light on right) show typical inclusion-rich staurolite and characteristic interference color and color in plane light. The picture below, under crossed polarizers, shows a large staurolite grain in a schist, surrounded by brightly colored muscovite and some quartz.

Occurrence

Staurolite occurs in regional dynamothermal metamorphosed shales, as porphyroblasts associated with garnet, biotite, muscovite, and possibly kyanite.


INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/mineral/m_19.gif" \* MERGEFORMATINET Stilpnomelane H2(Mg,Fe)Al2SiO7

Optical Properties:

Biaxial , but with 2V close to 0 degrees; extinction almost parallel; brown to yellow green pleochroism is distinctive.

The photographs above show golden stilpnomelane in plane polarized light (left) and under crossed polarizers (right). The photo below (uncrossed polarizers) shows stilpnomelane in a characteristic sheaf-like arrangement.

Occurrence:

Stilpnomelane occurs in some low grade, burial metamorphic rocks, with quartz, white mica, garnet, etc.


INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/rocks/r_3.gif" \* MERGEFORMATINET Dunite

Dunite contains over 90% olivine, typically with allotriomorphic-granular (gabbroic) texture. Dunites form during differentiation of mafic melts and as segregations in the mantle. They also occur as high temperature intrusions.

The photos above show anhedral olivine grains, partially altered around grain margins and along fractures to platy, highly birefringent talc.


INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/mineral/m_42.gif" \* MERGEFORMATINET Tourmaline Group Na-Fe-Mg-Li Al borosilicates

Optical Properties:

Uniaxial -; parallel extinction; color varies from colorless to pale yellow, pink green, blue, etc., depending on variety; color zoning is common; moderate birefringence, typically second order colors.

The photos above, under crossed polarizers, show tourmaline with quartz inclusions and surrounded by quartz (left picture), and zoned tourmaline crystals surrounded by muscovite in the picture on the right.

Occurrence:

Large crystals are found in granite pegmatites. Other occurrences are in high temperature veins, schists, and gneisses.


Tremolite-Actinolite Ca2(Mg,Fe)5(OH)2(Si4O11)2

Optical Properties:

Biaxial -; colorless to pale green in plane polarized light; amphibole cleavage (2 directions at 56 degrees); interference colors up to middle second order; inclined extinction; prismatic to fibrous form.

The photo above, under crossed polarizers, shows the moderate birefringence and cleavage of tremolite. The pictures below (crossed polarizers on the left, plane polarized light on the right) show a tremolite schist, composed almost entirely of tremolite. Interlocking fibers of tremolite form the jade mineral, nephrite.

INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/meta/dynamo/tremolite.photoshop" \* MERGEFORMATINET Occurrence:

Common in contact metamorphosed carbonate rocks; the Fe-rich member, actinolite, occurs in metamorphosed mafic rocks.


INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/mineral/m_53.gif" \* MERGEFORMATINET Calcite CaCO3

Optical Properties:

Uniaxial -; extreme birefringence, high order colors; common polysynthetic twinning; rhombohedral cleavage; symmetrical extinction; colorless in plane polarized light.

The photos above (left is plane polarized light, right under crossed polarizers) show the high birefringence, twinning, and cleavage typical of calcite.

The photograph below (crossed polarizers) shows calcite replacing plagioclase.

Occurrence:

Principal constituent of limestones and marbles; common alteration of other minerals and as a cement in sedimentary rocks.


Chalcedony SiO2

Optical Properties:

Chalcedony is very fine-grained quartz. It commonly occurs as radiating aggregates, as shown in the crossed polarizers view above. First order gray interference color, as in quartz; other optical properties generally are difficult to measure, because of the small grain size.

Occurrence:

Chalcedony occurs as a cement in some clastic sedimentary rocks, as replacement of calcite in come carbonates, and as vesicle fillings in some lavas.


Dolostone

Dolostone is a sedimentary rock consisting principally of dolomite. The photograph, under crossed polarizers, shows the extreme birifringence and twinning characteristics of dolomite. Dolomite is difficult to distinguish from calcite in thin section, without special treatment.


Glauconite KMg(Fe,Al)(SiO3)6.3H2O

Optical Properties:

Biaxial -; 2V 16-30 degrees; green to yellow pleochroism; excellent single cleavage; parallel extinction; often forms in pellets in sediments.

Occurrence:

Glauconite forms under reducing conditions in sediments and is commonly found in nearshore sandstones.


Carbonatite

Carbonatites are igneous rocks consisting of more that 50% carbonate minerals, such as calcite or dolomite. Subordinate minerals are biotite, olivine, clinopyroxene, etc.

The photograph is a cross-polarized view showing twinned, very highly birefringent calcite grains in an almost pure calcite carbonatite.


Clinopyroxenite

Clinopyroxenite is over 90% clinopyroxene. These rocks form as segregates during differentiation of mafic magma, and they are present in some ophiolites.

The picture above shows andhedral clinopyroxene grains, some with exsolution lamellae of orthopyroxene, and sutured grain boundaries.



Name: Diorite

In the photographs above, large, twinned plagioclase crystals and hornblende grains in a finer matrix provide porphyritic texture. Diorites contain less than 35% ferromagnesian minerals; plagioclase composition is typically An30-50. Diorites are common in I-type batholiths associated with subduction zones. They are the intrusive equivalents of andesites.


INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/intrus/a_37.gif" \* MERGEFORMATINET Gabbro

The photographs above are crossed polarizer views of gabbros. The brightly colored minerals are clinopyroxene, and the white to gray minerals are plagioclase. The black minerals in both pictures are opaque grains of magnetite. Gabbros have more than 35% ferromagnesian minerals, and plagioclase composition in greater than An50. Gabbro is the intrusive equivalent of basalt.

The photographs below (crossed polarizers) shows a gabbro with brightly colored and fractured olivine surrounded by plagioclase (left photo) and a gabbro with cumulate texture, plagioclase poikilitically enclosed by clinopyroxene.

INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/ultra/b_47.gif" \* MERGEFORMATINET Petrography Home Minerals List Rocks List

Granite The photograph above is under crossed polarizers. The field of view is about 4 mm. The mineral with numerous crossing twins is microcline. The clear (white), anhedral mineral is quartz. The partially altered, smaller grains are plagioclase, and the bright mineral in the upper right is biotite. This is a typical mineral assemblage in granites.

Occurrence:

Granites are abundant in continental shield areas and in deeply eroded folded mountain belts.


Granodiorite

The field of view in the photo is 4 mm across. The highly twinned mineral is plagioclase; the clear, untwinned, white to pale yellow mineral is quartz; orthoclase is the grain in the upper left corner; there is a hornblende grain (with high relief) in the upper right corner. The mineralogy of granodiorites is similar to that of granites, but granites contain more alkali feldspar.

Occurrence:

Granodiorites are abundant in orogenic batholiths.


Granophyre

Granophyres are alkali feldspar and quartz rocks that may represent the most differentiated portions of mafic intrusions. The granophyre in the photo above (field of view 1.5 mm) shows altered sodic plagioclase and clear quartz, in some cases intergrown to form myrmekite.

Occurrence:

Granophyres form small sills and dikes in highly differentiated, layered intrusions.


Keratophyre

Keratophyres are Na-rich extrusive rocks, containing pure sodic plagioclase with or without quartz.

Occurrence:

Keratophyre dikes and sills are found in some ophiolites, and keratophyre lava flows are present in some island arcs.

The photograph, under crossed polarizers, shows twinned albite plagioclase phenocrysts and microlites, with tiny quartz grains, in a glassy matrix.


Lherzolite

Lherzolites contain over 60% olivine, and some clinopyroxene and orthopyroxene. Lherzolite is a major constituent of the mantle and the source of most basaltic magmas.

The picture above (under crossed polarizers) shows olivine (right side of picture), orthopyroxene (lower left) and clinopyroxene (upper left), with characteristic allotriomorphic-granular texture.


Nepheline Syenite

This is a relatively rare rock, undersaturated in silica to the extent that nepheline forms in place of some feldspars. These rocks occur in both stable cratonic areas and as minor intrusions in orogenic provinces. The photograph above shows perthite (with typical stringy intergrowths), and in the lower center, a gray, clear, subhedral nepheline crystal.


Quartz Monzonite

Quartz monzonite, like granite, consists of quartz, K-feldspar, and plagioclase, with minor ferromagnesian minerals. It is a rather abundant rock type in many orogenic areas. In the photo above are multiply twinned plagiocase, bright white perthite, and clear quartz, with minor biotite.Petrography Home Minerals List Rocks List

Syenite

Syenite is an intrusive rock consisting principally of alkali feldspar, with little or no quartz or feldspathoid, and typically only small amounts of ferromagnesian minerals.

The photo above shows a field of view about 4 mm across, under crossed polarizers. Perthite is the only abundant mineral in the rock. The dark brown grains are biotite and minor hornblende.



Tonalite

Tonalite mineralogy is similar to that of granodiorite, but with little or no K-feldspar. The photos above (crossed polars on left, plane light on right) show a large grain of zoned, altered plagioclase in the lower right (partially altered to sericite and epidote), and large pleochroic crystals of biotite. The extinct (dark) areas in the upper left corner and lower left corner of the photo on the left are quartz crystals at extinction.

Occurrence:

Tonalite is a major component of many I-type batholiths.


Websterite

Websterite is a member of the peridotite family, containing both orthopyroxene and clinopyroxene, typically as anhedral grains. In the photo above, the brighly colored grains are clinopyroxene, and the grains with first order color are orthopyroxene.


INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/extrus/c_55.gif" \* MERGEFORMATINET Andesite

Andesites consist of intermediate composition plagioclase (typically, An30-50), and less than 35% of ferromagnesian minerals such as clinopyroxene, hornblende, or olivine. Andesites are most abundant in subduction-related arc volcanoes.

The photographs above (crossed polarizers on left, plane polarized light on right) show zoned and twinned plagioclase phenocrysts in a matrix of glass and plagioclase microclites. Plagioclase microlites are subparallel, producing trachytic texture.


INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/extrus/c_57.gif" \* MERGEFORMATINET Basalt

Basalt is the most abundant volcanic rock; it underlies ocean floors and forms voluminous outpourings (flood basalts) on several continents; it is also a major constituent of island arcs. The principal mineral constituents of basalt are plagioclase and pyroxene and/or olivine. Basalts are commonly porphyritic.

Both photographs above are under crossesd polarizers. On the left, gray and white plagioclase and brightly colored , tiny clinopyroxene grains are in a matrix of dark glass. On the right, plagioclase laths and more birefringent orthopyroxene are the principal phenocrysts.

The photos below (crossed polarizers on the left, plane polarized light on the right) show brightly colored, equant olivine and gray plagioclase phenocrysts in a fine-grained matrix of glass and clinopyroxene.

INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/extrus/c_60.gif" \* MERGEFORMATINET Petrography Home Minerals List Rocks List

Dacite

Dacite is a quartz-rich extrusive (volcanic) rock that contains abundant sodic plagioclase. Dacite is a minor constituent of many arc volcanoes.

The photo above shows euhedral light gray plagioclase (the bottom crystal is beautifully zoned) and rounded quartz phenocrysts, in a very fine-grained matrix of the same minerals.


Rhyolite

Rhyolites are quartz-rich volcanic rocks with abundant alkali feldspar (typically sanidine) and lesser plagioclase. Rhyolites are a volumetrically minor component of some volcanic arcs and occur as vast ash flows in some areas affected by tensional tectonics.

The light gray phenocrysts at the top of the photo above are sanidine; a quartz grain is near the bottom edge of the photo. Flow banding is clearly visible in the glassy matrix.


INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/rocks/r_14.gif" \* MERGEFORMATINET Tuff

Tuffs are explosively erupted volcanic material that is consolidated and lithified after deposition. Tuffs may contain lithic fragments, glass shards, and/or broken mineral grains and have pyroclastic texture.

The photos above (crossed polarizers on left, plane polarized light on right) show lithic crystal tuffs containing twinned, broken plagioclase clasts, and altered lithic clasts (right side of photos), in a matrix of very fine-grained material.


INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/rocks/r_16.gif" \* MERGEFORMATINET Welded Tuff

Welded tuffs are formed during violent volcanic eruptions; gas-charged material is expelled and deposited while still partially molten, so that the droplets become attached, or "welded" to one another. Typically, the weight of overlying tuff flattens pumice fragments and produces aligned grains and lithic fragments. Tuffaceous textures are commonly best viewed in plane polarized light, particularly if the matrix is glassy, so that grain outlines can be seen.

The photos above show welded tuffs with irregularly shaped, light gray glass shards and mashed pumice clasts in a glassy matrix.

The pictures below show (on the left) a plane polarized light view of a highly welded tuff with numerous glass shards and broken plagioclase grains, and on the right a crossed polarizers view showing extinct glass matrix, lithic clasts, and broken plagioclase grains.

INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/rocks/r_22.gif" \* MERGEFORMATINET Petrography Home Minerals List Rocks List

Arkose Sandstone

Arkoses are feldspar-rich sandstones (95% quartz), often representing reworked sedimentary deposits. The photo, under crossed polarizers, shows subrounded quartz grains cemented by quartz in optical continuity with the grains. Quartz overgrowths around individual grains are identifiable because of a thin veneer of hematite "dust" around some original grain boundaries.


Shale

Shales and mudstones are the most abundant sedimentary rock types. They consist principally of very fine-grained clays and other minerals.

The photo, under crossed polarizers, has a field of view of 0.3 mm. The white grains are quartz, and the dark matrix is a mixture of various clay minerals.


INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/meta/dynamo/b_104.gif" \* MERGEFORMATINET Amphibolite

Amphibolites are metamorphosed mafic rocks and consists principally of plagioclase and hornblende and/or clinopyroxene.

The photographs above (crossed polarized view on the left, plane polarized light on the right) show plagioclase (white, light gray), hornblende (strongly colored in right-hand photo), and moderately birefringent clinopyroxene. Note that in metamorphic rocks, plagioclase is typically xenoblastic (anhedral) and unzoned.


INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/meta/burial/a_96.gif" \* MERGEFORMATINET Eclogite

Eclogite is a metamorphic rock (of basaltic composition) consisting principally of pyrope garnet and omphacitic pyroxene.

The photos (plane polarized light on right, crossed polarizers on left) show isotropic, high relief garnet (black in the left picture) and aligned omphacite.


INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/meta/contact/px.hornfels.photoshop" \* MERGEFORMATINET Hornfels

Hornfels is the name given to fine-grained, non-foliated rocks formed by thermal (contact) metamorphism.

The two pictures above (both under crossed polarizers) show the typical random orientations and fine grain size of hornfels. The rock on the left falls within the hornblende hornfels facies, with hornblende and plagioclase; the rock on the right is in the pyroxene hornfels facies and contains plagioclase, cordierite (a few of the first order yellow grains), and biotite.


Marble

Marbles are metamorphosed limestone or dolostone. The photo (crossed polarizers) shows strongly twinned and highly cleaved calcite.


Phyllite

Phyllites are fine-grained metamorphic rocks with well developed foliation, or alignment of platy or elongate grains. Phyllites typically consist of micas, quartz, and sodic plagioclase, formed during recrystallization of shales during regional dynamothermal metamorphism.

The photo (crossed polarizers) shows strongly aligned, brightly colored muscovite, darker biotite, and light gray quartz and feldspars.


Quartzite

Quartzite is metamorphosed quartz-rich sandstones. The photo shows a quartzite under crossed polarizers. All of the grains are quartz; black spaces are holes in the thin section. Note that all grains are xenoblastic (anhedral), typical of quartz in metamorphic rocks.


INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/mineral/m_15.gif" \* MERGEFORMATINET Schist

Schists are coarse-grained metamorphic rocks with strong foliation or parallelism of minerals of platy or prismatic habit, such as the micas or amphiboles, developed by tectonic pressures.

The photos above (under crossed polarizers) are of garnet schists; on the left, extinct garnet is surrounded by strongly aligned muscovite and biotite; on the right, extinct garnet is surrounded by white mica and glaucophane.

More SchistsPetrography Home Minerals List Rocks List

INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/rocks/r_23.gif" \* MERGEFORMATINET Ophitic, Subophitic, and Intergranular Texture

Both photographs above are with crossed polarizers. On the left, optically continuous clinopyroxene poikilitically encloses plagioclase grains to produce ophitic texture. On the right, the groundmass of a basalt shows clinopyroxene and plagioclase crystals of about equal size, or subophitic texture. The photo below shows a basalt with intergranular texture (in plane polarized light), with tiny, equant clinopyroxene grains interstitial to plagioclase laths.

Intersertal Texture

The photo above shows plagiclase microclites in an interstitial glassy matrix, in plane polarized light. Black grains are magnetite.

INCLUDEPICTURE "http://sorrel.humboldt.edu/~jdl1/web.page.images/rocks/r_21.gif" \* MERGEFORMATINET Trachytic Texture

The photos above illustrate trachytic texture: subparallel alignment of plagioclase microlites in volcanic rocks, produced by flow.

Spinifex Texture

The photo (plane polarized light) shows clinopyroxene (titanaugite) crystals in radiating needle-like form, surrounded by a fine-grained matrix, producing spinifex texture in a rapidly cooled basalt.

Aegirine

Next Mineral

1. ppl aegirine north-south x10

2. ppl aegirine east-west x10

3. xpl birefringence x10

group

inosilicate

system

monoclinic

formula

NaFe3+Si2O6

optic sign

biaxial neg

2V

60 - 70 degrees

relief

high pos

min. index

1.750 / 1.836

color

brown, yellow, green

pleochroism

yes, green, yellow, brown

birefringence

0.040 - 0.060

cleavage

yes, {110} prismatic at about 85 degrees

elongation

yes

extinction

yes,inclined, symmetrical

extinction angle

0 - 20 degrees

alteration

fine-grained amphibole (uralitization) or chlorite

habit

prismatic (stubby to elongate), fibrous (finitization)

occurence

igneous (alkalic), metamorphic (schist), sedimentary (carbonate)

Albite

Next Mineral

1. xpl anorthitic; unzoned x10

2. xpl anorthitic; unzoned x10

group tectosilicate

system triclinic

formula NaAlSi3O8-Ca Al2Si2O8

optic biaxial pos / neg

Too-Vee 45 - 102

relief.1 low pos / neg

min. index 1.527 / 1.590

color colorless

pleochroism no

birefringence.1 0.007 - 0.013

cleavage yes {

elongation no

extinction inclined

angle ***

alteration sericite (fine-grained white mica), clay, or zeolite

habit.1 tabular, columnar

occurence igneous (granitic, felsic), hydrothermal (pegmatites), metamorphic (low grade)

TwoV 1 2 3

relief 1 4

pleochroism.2

birefringence 1 3 4 5 6 7

cleavage.2 {001} perfect, {010} good, {110} poor

Almandine

Next Mineral

ppl surrounded by quartz 10*

xpl qtz and plagioclase 10*

ppl inclusions and rimming 10*

xpl off of 1 edge of garnet 10*

group garnet

system isometric

formula Fe3Al2(SiO4)3

optic isotropic

Too-Vee 0

relief.1 high pos

min. index 1.770 / 1.820

color colorless

pleochroism no

birefringence.1 no

cleavage no

elongation no

extinction no

angle no

alteration chlorite, hornblend, epidote, and iron oxides

habit.1 euhedral (hexagonal, octagonal)

occurence igneous (volcanic, felsic), metamorphic (medium to high grade, pelite, mafic)

TwoV

relief 3

pleochroism.2

birefringence

cleavage.2

Andalusite

Next Mineral

ppl porphyroblasts 5*

xpl low birefringence 5*

ppl within minor crenulations 10*

xpl illmenite crenulated 10*

group aluminosilicate

system orthorhombic

formula Al2SiO5

optic biaxial neg

Too-Vee 71 - 88

relief.1 mod to high pos

min. index 1.629 /1.650

color colorless, pink, green

pleochroism yes


cleavage yes

elongation yes

extinction parallel, symmetrical

angle 0

alteration sericite, chlorite, sillimanite, kyanite

habit.1 prismatic, tabular, fibrous, anhedral

occurence metamorphic (low to medium grade, contact, regional), hydrothermal (pegmatites)

TwoV 2

relief 2 3

pleochroism.2 pink, green, yellow

birefringence 1 3 4 5 6

cleavage.2 {110} two good at right angles

Anorthite

Next Mineral

ppl coarse-grained laths 10*

xpl w/ CPX and OPX 10*

group feldspar

system triclinic

formula NaAlSi3O8-CaAl2Si2O8


Too-Vee 75 - 102

relief.1 low pos / neg

min. index 1.527 / 1.590

color colorless

pleochroism no


cleavage yes

elongation no

extinction inclined

angle ***

alteration sericite, clay minerals, zeolite


occurence igneous (mafic, ultramafic), metamorphic (carbonate), sedimentary

TwoV 2 3

relief 1 4

pleochroism.2


cleavage.2 {001} perfect, {010} good intersect at 94

Anorthoclase

Next Mineral

1. ppl anorthoclase x5

2. xpl anorthoclase x5

3. ppl anorthoclase x5

group tectosilicate

system triclinic

formula (K,Na)AlSi3O8

optic biaxial neg

Too-Vee 0 - 55

relief.1 low neg

min. index 1.519 / 1.536

color colorless

pleochroism no


cleavage yes

elongation no

extinction inclined

angle ***

alteration ***


occurence igneous (felsic)

TwoV 1 2

relief 4

pleochroism.2

birefringence 1 2 3

cleavage.2 ***

Apatite

Next Mineral

1. ppl basal sections x10

2. xpl basal sections x10

3. ppl long sections x10

4. xpl maximum birefringence x10

5. xpl parallel extinction x10

group phosphate

system hexagonal

formula Ca5(PO4)3(F,OH,Cl)

optic uniaxial neg

Too-Vee 0

relief.1 moderate to high pos

min. index 1.633 / 1.665

color colorless

pleochroism no


cleavage yes basal cleavage {0001}, v. poor prismatic cleav. {1010}

elongation yes

extinction parallel

angle 0

alteration not readily altered

habit.1 equant, prismatic, columnar

occurence igneous (accessory)

TwoV

relief 2 3

pleochroism.2

birefringence 1 2 3

cleavage.2 {0001} basal, poor, {1010} very poor

Augite

Next Mineral

ppl 5*

xpl 5*

ppl can see angle of extinction/inclined extinction = CPX 5*

xpl extinction position 5*

ppl plagioclase matrix 5*

xpl 5*

group pyroxene

system monoclinic

formula (Ca,Mg,Fe,Al)2(Si,Al)2O6

optic biaxial pos

Too-Vee 25 - 70

relief.1 high pos

min. index 1.664 / 1.771

color colorless, green, violet

pleochroism no

birefringence.1 0.018 -0.034

cleavage yes

elongation no

extinction inclined

angle 35 - 50

alteration uralite, serpentine, chlorite, biotite, carbonates

habit.1 equant, prismatic, columnar

occurence igneous (mafic)

TwoV 1 2

relief 3

pleochroism.2


cleavage.2 {110} typical pyroxene cleavage at 87

Biotite

Next Mineral

ppl coarse-grained porphyrblasts 5*

xpl discordant plagioclase 5*

1. ppl w/chlorite alteration x5

2. xpl w/chlorite alteration x5

3. ppl min. pleoch. haloes N-S x5

4. ppl max. pleoch. haloes E-W x5

5. xpl birefringence E-W x5

6. xpl birefringence N-S x5


8. xpl extinct

group mica

system monoclinic

formula K2(Mg,Fe)3AlSi3O10(OH,O,F)2

optic biaxial neg

Too-Vee 0 - 25


min. index 1.522 / 1.696

color brown, green, orange

pleochroism yes


cleavage yes {{ easily seen

elongation yes yesalong cleavage

extinction parallel, nearly parallel

angle 0 - 9

alteration commonly alters to chlorite and clay minerals

habit.1 columnar, tabular, platy

occurence metamorphic (contact, low to high grade), igneous

TwoV 1

relief 2 3

pleochroism.2 tan, green, brown

birefringence 9 12 13

cleavage.2 {001} perfect, controls fragment orientation

Calcite

Next Mineral

ppl rhombohedral sections 5*

xpl characteristic cleavage 5*

1. ppl secondary calcite x10

2. xpl secondary calcite x10

group carbonate

system hexagonal (triagonal)

formula CaCO3

optic uniaxial pos

Too-Vee 0

relief.1 mod neg to high pos

min. index 1.486 / 1.658

color colorless

pleochroism no

birefringence.1 0.172

cleavage yes {1

elongation no

extinction inclined, symmetrical

angle ***

alteration dolomite, quartz, opal, iron or manganese oxides

habit.1 granular, euhedral

occurence igneous (mafic), metamorphic (carbonate)

TwoV

relief 5 1 2 3

pleochroism.2

birefringence 9 13

cleavage.2 {1011} perfect rhombohedral

Chlorite

Next Mineral

ppl biotite/musc/chlorite abundant illmenite parallel to foliation with muscovite 10*

"xpl ""and biotite parallel

ppl good cleavage 5*

xpl strong interference colors 5*

ppl 5*

xpl 5*

1. ppl chlorite N-S x10

2. ppl chlorite E-W x10

3. xpl extinction position x10

4. xpl purple birefringence x10

5. ppl chlorite x10

6. xpl anomolous birefringence x10

group chlorite

system monoclinic

formula (Mg,Fe)5Al(Si3Al)O10(OH)8

optic biaxial neg / pos

Too-Vee 0 - 60


min. index 1.550 / 1.690

color green, colorless, blue

pleochroism yes


cleavage yes { cleavage on {001} controls fragment orientation

elongation no

extinction inclined

angle 0 - 9 (cleavage)

alteration fairly resistant to alteration, oxidation, clay

habit.1 columnar, tabular, platy

occurence metamorphic (low to medium grade), igneous (hydrothermal), sedimentary

TwoV 1 2

relief 2 3

pleochroism.2 green

birefringence 1 2 3 4 5 6 7


Chloritoid

Next Mineral

ppl 5*

xpl 5*

ppl min. pleochroism N-S 5*

ppl max. pleochroism E-W 5*

xpl max. birefringence 10*

xpl 10*

ppl 10*

group orthosilicate

system monoclinic

formula see properties

optic biaxial pos

Too-Vee 36 - 72

relief.1 high pos

min. index 1.705 / 1.740

color green

pleochroism yes


cleavage yes

elongation yes

extinction inclined

angle 10 - 25

alteration chlorite, sericite

habit.1 lathlike, tabular

occurence metamorphic (low to medium grade, regional), hydrothermal

TwoV 1 2

relief 3

pleochroism.2 green, blue, yellow

birefringence 1 2 3 4 5 6 7 8

cleavage.2 {001} perfect, {110} two imperfect

Cordierite

Next Mineral

xpl 10*

group tectosilicate

system orthorhombic

formula Mg2Al3(AlSi5)O18


Too-Vee 40 - 90

relief.1 low neg / pos

min. index 1.521 / 1.578

color colorless, blue

pleochroism yes


cleavage yes

elongation no

extinction parallel

angle 0

alteration pinite (chlorite, muscovite)

habit.1 anhedral, granular

occurence igneous (granitic), metamorphic (medium to high grade, contact, regional, pelite)

TwoV

relief

pleochroism.2 blue, violet, yellow

birefringence

cleavage.2 {010} fair, {100} and {001} poor

Epidote

Next Mineral

1. ppl epidote x20

2. xpl epidote x20

ppl two cleavages 20*

xpl zoned diopside 20*

ppl filling of vessicles 5*

xpl anomolous inter. colors 5*

ppl porphyroblastic augen 5*

xpl pressure shadows 5*

xpl 5*

group epidote

system monoclinic

formula CA2Fe3+Al2O(Si2O7)(SiO4)(OH))

optic biaxial neg

Too-Vee 64 - 90

relief.1 high pos

min. index 1.715 / 1.797

color colorless, green, yellow

pleochroism yes


cleavage yes {

elongation yes

extinction inclined

angle 25 - 40

alteration not readily altered (detrital grains in clastic sediments)

habit.1 tabular, granular, columnar

occurence igneous (accessory), hydrothermal, metamorphic (medium grade)

TwoV 2

relief 3

pleochroism.2 yellow, green

birefringence 5 6 7 8 9 10 11 12 13

cleavage.2 {001} perfect basal, {100} poor

Fayalite

Next Mineral

1. ppl fayalite x10

2. xpl fayalite x10

group olivine

system orthorhombic

formula (Fa,Fe2SiO4)

optic biaxial neg

Too-Vee 46 - 98

relief.1 high pos

min. index 1.636 / 1.879

color colorless, yellow

pleochroism yes


cleavage no (

elongation no

extinction parallel

angle ***

alteration iddingsite, chlorophaeite

habit.1 equant, granular

occurence igneous (mafic), metamorphic (carbonate)

TwoV 2 3

relief 3

pleochroism.2 yellow, orange, brown

birefringence 9 12 13

cleavage.2 ( {010}, {110} not seen in thin section )

Glaucophane

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group riebeckite

system monoclinic

formula Na2Mg3Al2Si8O22(OH)2

optic biaxial neg

Too-Vee 10 - 45

relief.1 mod to mod high pos

min. index 1.606 / 1.717

color blue

pleochroism yes


cleavage yes

elongation yes lent

extinction symmetrical, inclined

angle 0 - 21

alteration amphibole

habit.1 prismatic, columnar

occurence metamorphic (medium grade, regional)

TwoV 1 2

relief 2 3

pleochroism.2 blue, green, violet


cleavage.2 {110} amphibole cleavge at 55 and 125

Grossular

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ppl 20*

xpl 20*

group garnet

system isometric

formula Ca3Al2(SiO4)3

optic uniaxial / biaxial

Too-Vee 0 - 90

relief.1 high pos

min. index 1.735 / 1.770

color colorless

pleochroism no

birefringence.1 anomalous

cleavage no

elongation no

extinction ***

angle ***

alteration chlorite, hornblende, epidote, and iron oxides

habit.1 equant , euhedral

occurence metamorphic (carbonate,skarn)

TwoV 1 2

relief 3

pleochroism.2

birefringence

cleavage.2

Hedenbergite

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group pyroxene

system monoclinic

formula CaFeSi2O6

optic biaxial pos

Too-Vee 25 - 70

relief.1 high pos

min. index 1.664 / 1.771

color colorless, gray, brown

pleochroism yes


cleavage yes

elongation yes

extinction inclined, symmetrical

angle 35 - 48

alteration uralite (amphibole), serpentine, chlorite, biotite

habit.1 prismatic, bladed, acicular

occurence igneous(granitic, volcanic, mafic),metamorphic(medium to high grade, skarn)

TwoV 1 2

relief 3

pleochroism.2 green, blue, brown


cleavage.2 {110} pyroxene cleavage at 87

Hornblende

Next Mineral

1. ppl w/cleavage and opacite x5

2. xpl hornblende x5

3. xpl hornblende x5

4. ppl hornblende x10

5. ppl elongation east-west x5

6. ppl elongation north-south x5


8. xpl inclined extinction x5

9. ppl pleochroism x5

10. xpl pleochreoism x5

11. xpl birefringence x5

12. ppl alkali north-south x5

13. ppl alkali east-west x5

14. xpl alkali max. birefring. x5

group amphibole

system monoclinic

formula Ca,Mg,Fe,Al silicate

optic biaxial neg / pos

Too-Vee 35 -130


min. index 1.600 / 1.730

color brown, red, yellow

pleochroism yes yellow-green, brown


cleavage yes amphibole cleavages {110} intersect at 56 and 124

elongation yes

extinction symmetrical, parallel

angle 10 - 35

alteration biotite, chlorite, or other Fe-Mg silicates

habit.1 equant, columnar, prismatic

occurence igneous (intermediate), metamorphic (medium to high grade, carbonate)

TwoV 1 2 3

relief 2 3

pleochroism.2 green, yellow, brown


cleavage.2 {110} intersects at 56 and 124

Hypersthene

Next Mineral

" ""porphyroblast

ppl matrix 5*

xpl 5*

ppl 5*

xpl 5*

ppl 10*

1. ppl hypersthene east-west x5

2. ppl hypersthene north-south x5


4. xpl extinction x5

group pyroxene

system orthorhombic

formula (Mg,Fe)2Si2O6

optic biaxial neg

Too-Vee 50 - 132


min. index 1.649 / 1.788

color green, pink, brown

pleochroism yes


cleavage yes

elongation yes

extinction parallel, symmetrical

angle 0

alteration serpentine, talc, or fine-grained amphibole

habit.1 prismatic, columnar, tabular

occurence igneous (ultramafic, mafic), metamorphic (high grade)

TwoV 1 2 3

relief 2 3

pleochroism.2 pink, yellow, brown


cleavage.2 {210} prism faces intersect at 88

Jadeite

Next Mineral

group pyroxene

system monoclinic

formula NaAlSi2O6


Too-Vee 60 - 96

relief.1 mod to high pos

min. index 1.640 / 1.692

color colorless

pleochroism yes


cleavage yes

elongation yes

extinction parallel, inclined, symmetric

angle 32 - 55

alteration amphibole, analcime, nepheline

habit.1 columnar, fibrous, prismatic, tabular

occurence metamorphic (medium grade, regional)

TwoV 2 3

relief 2 3

pleochroism.2 green, yellow

birefringence 1 2 3 4 5 6 7 8

cleavage.2 {110} pyroxene cleavage at 87

Kaersutite

Next Mineral

group amphibole

system monoclinic

formula see properties

optic biaxial neg

Too-Vee 66 - 84

relief.1 high pos

min. index 1.670

color brown, yellow, reddish, greenish

pleochroism yeslowish, reddish, brownish


cleavage yes

elongation **

extinction ***

angle ***

alteration amphiboles, titanaugite, Fe-Ti oxides, chlorite

habit.1 columnar, tabular

occurence igneous (alkalic, volcanic)

TwoV

relief

pleochroism.2 ***

birefringence

cleavage.2 ***

Kyanite

Next Mineral

ppl 10*

xpl 10*

group aluminosilicate

system triclinic

formula Al2SiO5

optic biaxial neg

Too-Vee 78 - 84

relief.1 high pos

min. index 1.710 / 1.734

color colorless, blue

pleochroism yes


cleavage yes

elongation yes

extinction inclined

angle 0 - 30

alteration sericite, chlorite, andalusite, sillimanite

habit.1 bladed, columnar

occurence metamorphic (pelite, schist, gneiss) , hydrothermal (pegmatite),

TwoV 2

relief 3

pleochroism.2 violet, blue

birefringence 5 6 7

cleavage.2 {100} perfect, {010} good

Leucite

Next Mineral

1. ppl leucite x5

2. xpl leucite x5

group feldspathoid

system tetragonal

formula KAlSi2O6

optic uniaxial pos

Too-Vee 0

relief.1 low neg

min. index 1.508 / 1.511

color colorless

pleochroism no


cleavage no

elongation no

extinction incomplete

angle 0

alteration pseudoleucite (mixture of nepheline and K-spar)

habit.1 equant, pseudoisometric

occurence igneous (mafic and alkalic)

TwoV

relief 4

pleochroism.2

birefringence 1 2

cleavage.2 ( {110} not seen in thin section)

Magnetite

Next Mineral

1. ppl magnetite x20

2. ppl symplecite x10

3. xpl symplecite x10

group spinel

system isometric

formula FeFe2O4

optic opaque

Too-Vee 0

relief.1 ***

min. index ***

color opaque

pleochroism no

birefringence.1 no

cleavage no

elongation no

extinction no

angle 0

alteration hematite, limonite, goethite, lamellae of illmenite

habit.1 equant, anhedral, granular

occurence igneous (accessory), metamorphic (skarn), sedimentary

TwoV

relief

pleochroism.2

birefringence

cleavage.2 ( {111} parting but not visible)

Microcline

Next Mineral

1. ppl microcline x5

2. xpl microcline x5



group feldspar

system triclinic

formula (K,Na)AlSi3O8

optic biaxial neg

Too-Vee 65 - 88

relief.1 low neg

min. index 1.514 / 1.533

color colorless

pleochroism no


cleavage yes

elongation no

extinction inclined

angle 5 - 15

alteration sericite, clay

habit.1 equant, tabular

occurence igneous (felsic, plutonic), metamorphic (high grade)

TwoV 2

relief 4

pleochroism.2

birefringence 1 2 3

cleavage.2 {001} perfect, {010) good

Muscovite

Next Mineral

1. ppl relief and cleavage x10

2. xpl relief; cleavage; max bir x10

3. xpl parallel extinction x10

ppl 10*

xpl 10*

ppl 10*

group mica

system monoclinic

formula KAl2(AlSi3O10)(OH)2

optic biaxial neg

Too-Vee 30 - 47

relief.1 moderate pos

min. index 1.552 / 1.623

color colorless, pink, green

pleochroism no


cleavage yes

elongation yes

extinction parallel

angle 0 - 3

alteration not readily altered, clay minerals (sericite)

habit.1 columnar, tabular

occurence igneous (felsic), metamorphic (low to meduim grade, regional, pelite), hydrothermal

TwoV 1

relief 2

pleochroism.2

birefringence 9 13


Nepheline

Next Mineral

1. ppl nepheline x5

2.

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minerales (1)