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Common Rock Types. Colby Geology. Igneous Rocks. Classification based on composition and texture . COMPOSITION Principally the rock-forming minerals Olivine Pyroxenes Amphiboles Micas Feldspars Quartz. Constitute 95% of minerals in ALL igneous rocks. COMPOSITION.

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common rock types
Common Rock Types

Colby Geology

slide4

Igneous Rocks

Classification based on composition and texture.

COMPOSITION

Principally the rock-forming minerals

Olivine

Pyroxenes

Amphiboles

Micas

Feldspars

Quartz

Constitute 95% of minerals in

ALL igneous rocks.

slide5

COMPOSITION

You can determine basic igneous rock composition

just by the COLOR of the rock.

DARK COLORED igneous rocks = MAFIC

LIGHT COLORED igneous rocks = FELSIC

GRAY COLORED igneous rocks = INTERMEDIATE

Color allows an approximation of igneous rock

composition

Related to Bowen’s Reaction Series

(red vs. green)

slide6

1200°C

Gabbro-Basalt

900°C

Diorite-Andesite

Granite-Rhyolite

600°C

slide7

TEXTURE

TEXTURE reflects cooling rate of magma or lava.

SLOW COOLING = LARGE Crystals

RAPID COOLING = SMALL Crystals

SLOW COOLING = PLUTONIC

RAPID COOLING = VOLCANIC

slide8

TEXTURE

Types of Textures

Phaneritic

Large crystals > 2 mm

Slow cooling rate = Plutonic

Granite, Diorite, Gabbro

Light Gray Dark

Felsic Intermediate Mafic

slide9

TEXTURE

Types of Textures

Aphanitic

Small crystals < 2 mm

Fast cooling rate = Volcanic

Rhyolite, Andesite, Massive Basalt

Felsite Scoria

Light Gray Dark

Felsic Intermediate Mafic

slide10

Rhyolite

Felsite

slide13

TEXTURE

Types of Textures

Glassy

No crystals, lava cools too fast

Extremely fast cooling rate = Volcanic

Obsidian,

Pumice

Light

Felsic

Pumice

Obsidian

slide14

TEXTURE

Types of Textures

Porphyritic

Two distinct sizes of crystals

Starts cooling slowly, remainder cools quickly

Phenocrysts

Groundmass

slide15

TEXTURE

Types of Textures

TEXTURE is related to origin of magma or lava.

Phaneritic = Coarse-grained = Intrusive

Plutonic

Aphanitic = Fine-grained = Extrusive

Glassy or smaller Volcanic

Identification/Classification of Igneous Rocks

Key on page 75-77 in lab manual

Chart on page 91 in lab manual

slide16

IGNEOUS ROCK CLASSIFICATION

COMPOSITION

PHANERITIC

APHANITIC

GLASSY

slide18

Sedimentary Rocks

Clastic Sedimentary Rocks

COMPOSITION

Derived from pre-existing rocks.

Five main constituents:

Quartz

Feldspar

Rock fragments

Clay (and clay minerals)

Calcite

slide20

Sediment Size

(mm)

Particle Name

Rock Name

>256

Boulder

64-256

Cobble

Conglomerate

Breccia

Gravel

4-64

Pebble

Granule

2-4

0.063-2

Sand

Sandstone

0.004-0.063

Silt

Siltstone

Mudstone

Mud

<0.004

Clay

Shale

TEXTURE

CLASTIC – fragments of rock debris

Classified by analyzing grain-size

slide21

Particles

>2mm = coarse-grained CONGLOMERATE

(rounded clasts)

BRECCIA

(angular clasts)

1/16 - 2mm = medium-grainedSANDSTONE

<2mm = fine-grainedSHALE

Sandstones further classified on the basis of their

mineralogical composition:

Mostly quartz = QUARTZ SS.

>25% feldspar = ARKOSE

1/3 silt, clay and rock fragments = GREYWACKE

slide23

Medium-grained Clastic Sedimentary Rocks

Sandstones

Arkose

Greywacke

Qtz. Sandstone

slide25

Sedimentary Rocks

Chemical Sedimentary Rocks

CHEMICAL SEDIMENTARY ROCKS

precipitated from sea water (evaporites)

initially dissolved in water

very similar in appearance to igneous rocks

exceptMONOMINERALIC.

texture is crystalline if visible

microcrystalline if not

OOLITIC LIMESTONE

CHERT

DOLOMITE

slide29

CHEMICAL SEDIMENTARY ROCKS

ROCK SALT or HALITE

composed of halite (NaCl)

microcrystalline to crystalline

precipitates from sea water

forms economic deposits

slide30

Sedimentary Rocks

Organic Sedimentary Rocks

ORGANIC or BIOCLASTIC SEDIMENTARY ROCKS

can be crystalline or clastic (bioclastic)

all particles are derived from organisms

typically composed of calcite or aragonite (CaCO3)

slide31

Lithographic Limestone or Micrite

Very fine-grained limestone

Formed from calcareous

algae

Fizzes in HCl

slide33

NONCARBONATE ORGANIC SED. ROCKS

CHERT

microcrystalline

composed of skeletons, microscopic in size

made of SiO2

hardness = 7

may exhibit conchoidal fracture

slide34

NONCARBONATE ORGANIC SED. ROCKS

PEAT

composed of compressed plant debris

basic building block of coal

used as a fuel source in some areas

slide35

Identification/Classification of Sedimentary Rocks

Key on page 79-80 in lab manual

Chart on page 93 in lab manual

slide36

Metamorphic Rocks

Rocks are fundamentally changed by HEAT and/or

PRESSURE

May be derived from ANY pre-existing rock type

CLASSIFICATION

based on the presence or absence of FOLIATION

FOLIATION is the parallel alignment of the tabular

minerals (micas and clay minerals) and by

varying degrees of banding.

slide40

Metamorphic Rocks

Types of Foliation

Slatey cleavage

very fine-grained rocks

Usually found in slate and phyllite

slide41

Metamorphic Rocks

Types of Foliation

Schistosity

platy minerals visible

Usually found in schist

slide42

Metamorphic Rocks

Types of Foliation

Gneissic banding

minerals segregated into bands

Usually found in gneiss

slide43

Metamorphic Rocks

Foliated Rocks

SLATE Have slatey cleavage

PHYLLITE Rock splits along parallel planes

SCHIST Has schistosity

GNEISS Has gneissic banding

slide44

Metamorphic Rocks

Nonfoliated Rocks

NO structure is apparent in the rock

Rock is typically MASSIVE (monomineralic)

slide45

Metamorphic Rocks

Nonfoliated Rocks

MARBLE

Is composed of calcite (CaCO3), soft H = 3

Will react to dilute hydrochloric acid

slide46

Metamorphic Rocks

Nonfoliated Rocks

QUARTZITE

Metamorphosed quartz sandstone

Hardness = 7

slide47

Metamorphic Rocks

Nonfoliated Rocks

ANTHRACITE COAL

Formed from organic material (plant debris)

Contains no minerals

slide48

Metamorphic Rocks

Nonfoliated Rocks

GREENSTONE

Composed of metamorphosed mafic igneous rocks

slide49

Identification/Classification of Metamorphic Rocks

Key on page 82 in lab manual

Chart on page 95 in lab manual