Copia de Petrography Flow Chart Final

Guided Discovery and Scoring Rubric for Petrographic Analysis of a Thin SectionSample #:

Geologic Context:

Igneous/sedimentary/metamorphic?Sample location? Geologic settingRock typeOther useful information?

Microscope Set-up Key Observations

Notes: List the different types of minerals that you will need to identify. Annotate your sketch or photo.


What do you know about this sample? (This will help you use your knowledge of geology to determine what minerals may be present, or must be excluded)

1. Low Power, PPL Reconaissance

What do you see? How many different minerals are evident? Note different minerals distinguished by: large v. small, shape--platy, equant, prismatic, etc. Do some minerals show distinctive colors? A sketch might be useful.

2. Low Power, XN Reconaissance

What do you see now? Note different mineral types with these properties: isotropic v. anisotropic; high v. low birefringence; parallel v. inclined extinction. What interesting textures do you see: e.g. alignment of grains; inclusions of one mineral in another; minerals that appear to replace or overgrow another.

Insert Sketch or Photomicrograph

Scale:


Scale:


Scale:

Guided Discovery and Scoring Rubric for Petrographic Analysis of a Thin Section

3. Mineral Identification

A. Opaque Minerals--describe the shape and occurrence of all opaque mineralsMicroscope Set-Up Plane Polarized Light

Describe: Habit Crystal Form

Opaque 1

Opaque 2

Notes and Sketch:

B. Isotropic Minerals--describe the properties of any isotropic mineralsMicroscope Set-Up Cross Polarized Light

Mineral Name

Iso 1:

Iso 2:

Notes and Sketch:

Habit, form, shape

Cleavages; how many, what angles?

Relief: high, med, low

Scale:

Scale:

Notes and Sketch:

Scale:


A. Opaque Minerals--describe the shape and occurrence of all opaque minerals

Occurrence (inclusions, disseminated…)

Notes and Sketch:

B. Isotropic Minerals--describe the properties of any isotropic minerals

Notes and Sketch:

Other: Color, occurrence (vein, porphyroblast, etc).


Scale:


Scale:

Notes and Sketch:

Scale:


3. Mineral Identification--Anisotropic MineralsC. Primary Minerals (Paragenesis)

Mineral 1 Name:

Physical Properties Habit/Form/Shape Other

Optical Properties Uniaxial/Biaxial Optic Sign (+ or -) 2V (if biaxial)

Relief (high, med,low) Pleochroism/Color

Length Fast/Slow Twins--type Compositional Zoning Other

Notes and Sketch:

Mineral 2 Name:





Notes and Sketch:

Cleavage; How many; Angles

Birefringence (high med low, 1º 2º 3º…color)

Extinction Angle; parallel, inclined, symmetrical




Notes and Sketch:


3. Mineral Identification--Anisotropic MineralsC. Primary Minerals (Paragenesis)

Mineral 3 Name:





Notes and Sketch:

Mineral 4 Name:





Notes and Sketch:







Notes and Sketch:


3. Mineral Identification--Anisotropic MineralsC. Primary Minerals (Paragenesis); Anisotropic minerals;

Mineral 5 Name:





Notes and Sketch:

Mineral 6 Name:





Notes and Sketch:







Notes and Sketch:


3. Mineral Identification--Anisotropic MineralsD. Accessory Minerals: zircon, apatite, titanite,…

Mineral 1 Name:





Notes and Sketch:

Mineral 2 Name:





Notes and Sketch:







Notes and Sketch:


3. Mineral Identification--Anisotropic MineralsD. Accessory Minerals--zircon, apatite, titanite, ….

Mineral 3 Name:





Notes and Sketch:

Mineral 4 Name:





Notes and Sketch:







Notes and Sketch:


3. Mineral Identification--Anisotropic MineralsD. Alteration or Retrograde Minerals--sericite, chlorite, carbonate….

Mineral 1 Name:





Notes and Sketch:

Mineral 2 Name:





Notes and Sketch:








3. Mineral Identification--Anisotropic MineralsD. Alteration or Retrograde Minerals--sericite, chlorite, carbonate,….

Mineral 3 Name:





Notes and Sketch:

Mineral 4 Name:





Notes and Sketch:







Notes and Sketch:


Igneous Petrography

Sample #:Geologic Context:

Sample location?

Geologic setting?

Rock type or association, if known?

Other useful information?

1. General Textural Characteristics

Holocrystalline

B. Grain Size

(Shape of individual grains and relationships between grains)

Based on H. Williams, F.J. Turner, C. M., Gilbert, (1982), Petrography An Intrdocution to the Study of Rocks in Thin Sections, 2nd Ed., p. 53-67 and 79-89.

Before you start: What do you already know about this sample? This will help you use your knowledge of geology to determine what minerals may be present, and what textures are significant to interpret geologic processes and history.

The following observations could or should be made for any petrographic analysis of an igneous rock. This guide will help you to ask the appropriate questions, and seek the answers, that will lead you to the comprehensive description of a thin section that is needed to interpret geologic processes and history.

A. Degree of Crystallinity: Is this rock

Amorphous (glassy)Does it have minute tabular crystals, microlites

Aphanitic (not visible to the naked eye) Microcrystalline (observed with a microscope) Phaneritic (grains observable with hand lens) Uniform grain size, < 1 mm, fine-grained Uniform grain size, between 1-5 mm, medium grained Uniform grain size, between 5 mm- 3 cm, coarse grained Uniform grain size, > 3 cm, very coarse grained

C. Igneous Fabrics

Euhedral, grains entirely bounded by rational crystal facesSubhedral, grains partly bounded by rational crystal faces

Notes:


Scale:

D. Some Specific Igneous Textures to Look For

Inequigranular TexturesPorphyritic Texture

Intergrowths

Exsolution

Some Reaction Textures

Some Textures in Volcanic Rocks/Lavas

Glass, Pumice, Fiamme

Matrix Grains

Anhedral, Devoid of crystal faces, irregular shapes

Equigranular, equidimensional, equant grains of uniform size

Subhedral granular, some grains w/ eu-, sub-, and anhedral (also called granitic, or hypidiomorphic-granular) Anhedral granular, most grains are anhedral

Fine grained "groundmass" or matrix is present Distinctly larger phenocrysts are presentMicroporphyritic--phenocrysts must be seen with 'scopeSerrate porphyritic--continuous variation in grain sizeHiatal porphyritic--two distinct populations of grain sizesGlomeroporphyritic--phenocrysts in clustersVitrophyric, phenocrysts lie in glassy matrix

Cumulate Textures--aggregate of grains accumulated due to crystal settling

Intercumulus--minerals from interstitial melt in final stages of crystallization

Graphic, cuniform intergrowth of quartz and Kspar

Myrmekite, "wormy" intergrowths of quartz in sodic plag; replacement of potassic feldspar at contacts with plag.Ophitic, plag laths enclosed in large sub-hedral pyroxene

Poikilitic, randomly oriented grains entirely enclosed by loptically contiuous crystals of another composition

Perthite--lamellae of plagioclase in Kspar Anti-perthite--laemellae of Kspar in plagioclase "Inverted Pigeonite"--oriented cpx lamellae in opx

Relict minerals--remnants of an early stage of crystallization that have not been completely replaced Coronas or Reaction Rims--early-stage grains surrounded by later overgrowths in a reaction series

Intergranular--small grains fill interstices

Intersertal--interstices are filled with glass or secondary mineralsHyalopilitic--glass occupies interspaces between microlites Pyroclastic--fractured appearance of grains

Felty--microlites of plag, irregularly oriented in matrix Trachytic--sub-parallel orientation of microlites in matrix

Notes:



Notes:

Notes:

Scale:

Scale:

2. Petrographic Classification of Igneous Rocks

B. Modal Mineralogy An%1 Phenocrysts2 Zoning

3

45 Oscillatory6 Groundmass7 D. Phenocryst %89 E. Alteration/Retrograde Minerals10 1

TOTAL 2 3G. Volcanic Fragments 4 Pumice F. Accessory Minerals Glass shards 1 Fiamme (bent and flattened glass) 2

3

Vesicular--spherical or ovoid cavities in rockAmygdaloidal--vesicles filled with secondary mineralsDrusy or Mariolitic--terminated crystals grow into vesicles

A. Color Index (CI): Ratio of dark to light colored minerals; estimated visually or determined by point count

% Estimated or Point Count

C. Plagioclase Composition

Normal (Anx - Any)

Reverse (Any-Anx)

Notes:

Plot the composition on this ternary diagram; label the apices; draw the appropriate fields from the IUGS classification.

IUGS Igneous Classification, Streckeisen (1976)

Gabbroic Rocks

Ultramafic Rocks

Plutonic Felsic Rocks

Volcanic Felsic Rocks

Diagram used to Estimate the proportion components and matrix.



Sample location?

Geologic setting?



Clastic TexturesGrain-supportedMatrix-supportedGrain Size

Sorting

Grain Shape Rounded Subrounded Subangular Angular Spheroidal or Round Disc-shaped or Platy PrismaticGrain Orientation

Sedimentary Petrography-- Clastic Rocks

Based on H. Williams, F.J. Turner, C. M., Gilbert, (1982), Petrography An Intrdocution to the Study of Rocks in Thin Sections, 2nd Ed., p. 300-314; 325-362


Very Coarse 2 mm-1 mm Coarse 1 mm to 0.5 mm Medium 0.5 mm to 0.25 mm Fine 0.25 mm to 0.125 mm Very Fine--0.125mm-.05 mm

Well-sorted--all grains are of the same size Poorly-sorted--a continuum of grain sizes

Laminae--stratification on a mm-scale Graded--grain size varies progressively from top to bottom Cross-lamination--depostion from small ripples Convolute lamination--graded layers deposited in turbidity currents


Scale:

Notes:

Sandstone Classification

Grain/Clast Type% Quartz %

Framework (grain-supported) Feldspars (Plag + Kspar) %Cements (Authigenic Minerals) Lithic Fragments % Quartz % Chert/chalcedony % Chalcedony % Volcanic glass/pumice % Calcite % Micas % Other Carbonate (dol, sid, ank) % Metamorphic mins % Phyllosilicate (kaol, chlor, smect) % Other: % Gypsum, anydrite % Other: % Hematite/FeOx % Other: % Other… % TOTAL %

%%

Detrital Accessory Minerals Zircon Apatite Fe-Oxides (magnetite, ilmenite) Tourmaline Titanite (sphene)

Other

Imbricate--grains roughly parallel, but slightly dipping with respect to layering

% Grains* Estimated or Point Count

Argillaceous Matrix (matrix-supported)

* Note: This is an estimate of relative % of grains present, i.e. in a point count every grain is counted only once; this is in contrast with modal estimates of igneous rocks where the point count is done on a grid to estimate relative volume % (i.e. large phenocrysts will be counted multiple times.

Relative proportions of quartz (Q), feldspars (F), lithic fragments (L), and matrix (M) will be used to classify rocks in the family of sandstones: arenite, lithic arenite, felspathic arenite, arkose, subarkose, etc. See diagrams on next page.

Porosity (current % open pore space)Primary porosity (% open+%cement)

Other

Notes:


Scale:

Notes:



Sample location?

Geologic setting?


Non-clastic Textures (Crystalline)

Limestones

Rock Name:

(use chart on next page)MATRIX % of Total RockMicrocrystalline calcite % Mud-supportedSparry calcite % Grain-supported

GRAIN TYPES (Allochems) Skeletal grains (fossils) % Ooids % Pellets % Intraclasts %

TOTAL %

Sedimentary Petrography--Limestones

Based on H. Williams, F.J. Turner, C. M., Gilbert, (1982), Petrography An Intrdocution to the Study of Rocks in Thin Sections, 2nd Ed., p. 363-397.



Crystalline granular-- equant, uniform sizeMicrocrystalline--individual grains can't be seen with eye; ~30 microns

Crytpocrysalline--grains can't be seen in microscope; X-ray needed


Scale:

Notes:

Types of Fossils:



Sample location?

Geologic setting?


Mineral Paragenesis % 123456

Retrograde/Replacement %1234

Accessory Minerals % Possible Geothermobarometers; Exchange, Net Transfer; Gt-Bio, GASP1234

Metamorphic Petrography

Based on H. Williams, F.J. Turner, C. M., Gilbert, (1982), Petrography An Intrdocution to the Study of Rocks in Thin Sections, 2nd Ed., p. 438-452;.



Evidence of Metamorphic Reactions: (e.g. garnet + chlorite = biotite + staurolite)


Scale:

Metamorphic Textures

Shapes of Individual Crystals

Mosaic, or granoblastic Foliations (how many and what types?)

Grain size layering

Slaty cleavage Lineations

Rods Mineral aggregates Boudinage

Mylonites S-C mylonite

C-C' mylonite

Microfolds

Cataclastic Structures Flater structure Mortar structure Augen structure

NOTES:

Porphyroblast--large grains in matrix Idioblastic--grains with rational crystal faces Hypidoblastic-- some grains with Xtal faces Xenoblastic--no regular crystal faces Lepidobalastic--aligned platy minerals Poikiloblastic--small grains in larger porphyro.. Decussate--random arrangement of minerals

Gneissic--compositional layering (define scale)

Schistosity--parallel alignment of micas

Mineral (alignment of hbld, sillimanite, etc.)

Kinematic indicator ("fish". Σ, δ…)

crenulation, isoclinal, open, polyphase….. Insert Sketch or Photomicrograph

Scale:

The CaO-MgO-SiO2 Diagram

AFM Diagram for Pelitic Rocks

ACF Diagram for Mafic Rocks

Metamorphic Rock Classification

Foliated Rocks Unfoliated Rocks slate hornfels phyllite granofels schist skarn gneiss

Metabasites migmatite greenschist

amphibolite blueschist eclogite granulite

http://pubs.usgs.gov/of/2004/1451/sltt/appendixB/appendixB.pdf



Sample #:

Possible Geothermobarometers; Exchange, Net Transfer; Gt-Bio, GASP

Based on H. Williams, F.J. Turner, C. M., Gilbert, (1982), Petrography An Intrdocution to the Study of Rocks in Thin Sections, 2nd Ed., p.


(e.g. garnet + chlorite = biotite + staurolite)


Protoliths

Ultramafic Mafic or Basite Pelitic Semi-pelitic or Psammitic Carbonate Quartofeldspathic Other (e.g. BIF, Manganiferous….)

Relict Textures

Igneous: porphyritic, ophitic, etc. Sedimentary: bedding, pebbles, fossils… Metamorphic, banding, foliation, porphyroblasts

Timing of Grain Growth w/ Respect to Deformation Pre-kinematic Syn-kinematic Post-kinematic

Cataclastic Structures Flaser Structure Mortar Structure Augen structure

Recrystallization Granoblastic--equant, straight grain boundary Hornfels--recrystallized by contact metamorphism

Para--sedimentary originOrtho--igneojus origin


Scale:

AFM Diagram for Pelitic Rocks

ACF Diagram for Mafic Rocks

Other Metamorphic Rocks marble quartzite serpentinite banded iron formation

High Strain Rocks breccia, gouge mylonite, proto-, ultra-, blasto- pseudotachylite



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Copia de Petrography Flow Chart Final