Granitic pegmatite FelsicGranite, granodiorite, rhyolite,
rhyodacite, etc. IntermediateDiorite, tonalite, andesite, dacite,
etc. MaficGabbro, basalt, dolerite, scoria, tachylyte, etc.
UltramaficNorite, peridotite, anorthosite, komatiite, etc
Si-deficientSyenite, foyaite, phonolite, etc.
Slide 3
Slide 4
Minerals in this rock include quartz, plagioclase, biotite, and
K-feldspar.
Slide 5
Micrographic quartz and K-feldspar (cuneiform shaped
intergrowths) dominate this rock.
Slide 6
This crystal-rich rhyolite contains phenocrysts of quartz, K-
feldspar (sanidine), plagioclase, and biotite in a fine-grained
groundmass. Note the interesting shape of the (partially resorbed)
quartz grain in the center of the photograph.
Slide 7
This rock contains hornblende, plagioclase clinopyroxene,
biotite, and quartz. Notice how the hornblende rims the small core
of relict clinopyroxene in the center of this photo, indicating a
reaction relationship.
Slide 8
A diabase is a mafic rock with grain size more or less
transitional between gabbro (coarse) and basalt (fine). Notice the
elongate lath-shaped plagioclase and the colorful clinopyroxene and
possible olivine in this rock.
Slide 9
Plagioclase and hypersthene (orthopyroxene) dominate this rock.
This slide may have been cut a little too thick, accounting for the
higher-than- expected interference colors of the hypersthene.
Slide 10
A norite is a gabbro in which the pyroxene is principally
orthopyroxene. This norite from the uppermost portions of the
famous Stillwater Complex in Montana also contains some
clinopyroxene. Generally, clinopyroxene has higher interference
colors than orthopyroxene, as shown in this photomicrograph.
Slide 11
This rock is composed almost entirely of albitic
plagioclase.
Slide 12
This rock is dominated by the clinopyroxene augite.
Slide 13
Bronzitite is an orthopyroxenite dominated by the mineral
hypersthene. Almost all of the grains in this photomicrograph are
hypersthene. This rock also contains some interstitial plagioclase
better seen in plane light.
Slide 14
Almost all of the grains in this rock are olivine. Note the
high order interference colors of olivine and the minor secondary
calcite which occurs as veinlets through the sample.
Slide 15
Thin sections of foyaite, a nepheline syenite, with some
plagioclase, microcline and nepheline
Slide 16
Thin section of syenite., with some plagioclase and
clinopyroxene, but also biotite and heavy residua of K- Feldspar.
This is presumably a plag-rich syenite.
Slide 17
Slide 18
In this photomicrograph, euhedral to subhedral biotite and
plagioclase crystals are surrounded by optically-continuous,
gray-colored K-feldspar.
Slide 19
Figure 3.7. Euhedral early pyroxene with late interstitial
plagioclase (horizontal twins). Stillwater complex, Montana. Field
width 5 mm. John Winter and Prentice Hall.
Slide 20
Figure 3.8. Ophitic texture. A single pyroxene envelops several
well-developed plagioclase laths. Width 1 mm. Skaergrd intrusion,
E. Greenland. John Winter and Prentice Hall.
Slide 21
Slide 22
The light gray streaks in this photomicrograph are plagioclase
exsolution lamellae in gray K-feldspar. Perthite forms as an
originally homogeneous feldspar exsolves two feldspars as
temperature falls below the feldspar solvus during subsolidus
cooling.
Slide 23
Myrmekitic texture defined by wormy (rounded) intergrowths of
quartz and K-feldspar in plagioclase. Probably forms as a result of
subsolidus exchange. Compare this texture to micrographic
texture.
Slide 24
Slide 25
This breccia is composed of fragments of a variety of volcanic
materials.
Slide 26
Komatiites are rare ultramafic volcanic rocks. This sample
displays the characteristic "spinifex texture" defined by extremely
acicular olivine phenocrysts--probably a sign of rapid
crystallization from a significantly-undercooled magma.
Slide 27
Scoria is another name for a highly-vesicular (almost "frothy")
basalt. The black, ovals features in this photomicrograph are
vesicles. Note the acicular, white plagioclase laths throughout and
the euhedral, white olivine phenocryst at the lower right.
Slide 28
After hydrothermal alteration of vesicles in scoria: The oval
feature in this photomicrograph is an amygdule: a formerly open
vesicle which has been filled with a secondary mineral(s)
precipitated from low-T ground waters which have penetrated into
the rock. In this case, the amygdule is probably filled with a
zeolite mineral.
Slide 29
Spherulites are radiating masses of fibrous crystals in a
glassy matrix. These spherulites are probably composed of alkali
feldspars and some polymorph of SiO2, and in this cross-polarized
shot, appear as round objects with dark crosses. Note the large
phenocryst which forms the nucleus of one of the spherulites at
center-left.
Slide 30
A vitrophyre is another name for a phenocryst- bearing
obsidian. The phenocrysts in the above photomicrograph are mostly
plagioclase. The groundmass is obsidian glass.
Slide 31
PeliticMetamorphosed shale: slate, phyllite, mica schist,
hornfels MaficMetamorphosed mafic rocks and their sediments
Carbonate and calc-silicateMetamorphosed limestone, dolostone and
calcareous sediments Metagraywacke (High P/LowT)Zeolite and
blueschist facies rocks Granitic gneissMetamorphosed arkosic
sediments, granite, rhyolite, etc.)
Slide 32
Slide 33
Typical textures of contact metamorphism. From Spry (1969)
Metamorphic Textures. Pergamon. Oxford.
Slide 34
Sandstone texture Quartzite texture
Slide 35
Typical textures of regional metamorphism: Types of foliations
a. Compositional layering b. Preferred orientation of platy
minerals c. Shape of deformed grains d. Grain size variation e.
Preferred orientation of platy minerals in a matrix without
preferred orientation f. Preferred orientation of lenticular
mineral aggregates g. Preferred orientation of fractures h.
Combinations of the above Figure 23.21. Types of fabric elements
that may define a foliation. From Turner and Weiss (1963) and
Passchier and Trouw (1996).
Slide 36
The crystal structure of this quartz grain has been deformed
(probably by low-grade metamorphism) to produce sub-grains.
Slide 37
Progressive syntectonic metamorphism of a volcanic graywacke,
New Zealand. From Best (1982). Igneous and Metamorphic Petrology.
W. H. Freeman. San Francisco. Foliation develops due mostly to
shear
Slide 38
Progressive syntectonic metamorphism of a volcanic graywacke,
New Zealand. From Best (1982). Igneous and Metamorphic Petrology.
W. H. Freeman. San Francisco. Fine-grained schist
Slide 39
Progressive syntectonic metamorphism of a volcanic graywacke,
New Zealand. From Best (1982). Igneous and Metamorphic Petrology.
W. H. Freeman. San Francisco. Well developed schist with coarser
grains
Slide 40
Figure 23.24a. Symmetrical crenulation cleavages in
amphibole-quartz-rich schist. Note concentration of quartz in hinge
areas. From Borradaile et al. (1982) Atlas of Deformational and
Metamorphic Rock Fabrics. Springer-Verlag.
Slide 41
Syn-kinematic crystals Figure 23.38. Snowball garnet with
highly rotated spiral S i. Porphyroblast is ~ 5 mm in diameter.
From Yardley et al. (1990) Atlas of Metamorphic Rocks and their
Textures. Longmans.
Slide 42
Photomicrograph of multiple reaction rims between olivine
(green, left) and plagioclase (right).
The feldspars in this alaskite from the Boulder Batholith have
been largely replaced by fine-grained white mica (sericite).
Slide 50
Weak alteration of the plagioclase feldspar known as
saussuritization is seen in this photomicrograph, the grain is also
rimmed by fine grained iron- oxyhydroxide precipitating from
solution.
Slide 51
Irregular linear alteration of olivine (O) to serpentine (S).
Several steps can be recognized PPL.
Slide 52
Photo 6.46 - Same as 6.45. Notice that fragments belonging to
the same original olivine crystal have identical interference
colors, showing their optical continuity . XPL. Photo 6.46 - Same
as 6.45. Notice that fragments belonging to the same original
olivine crystal have identical interference colors, showing their
optical continuity . XPL