Geology Lab Exam 1 UARK

Phyllite
(Metamorphic)

Phyllite
(Metamorphic)

Hardness: 1-2
Color: Black to Grey, Light Greenish Grey
Streak: White
Texture: A fine-grained metamorphic rock with a strong sheen
Mineral Composition: Chlorite, Muscovite, Biotite, Quartz, may have feldspar

Crinkled or wavy appearance.

Potassium Feldspar (Orthoclase)

Streak: White/Light Gray
Hardness: Harder than glass
Cleavage: Present

Usually Pink (sometimes white)
H=6 C=2 directions @ 90. (blocky)
Pearly luster

Diorite
(Igneous)

Coarse-grained igneous rock of intermediate composition. Up to half of the rock is plagioclase feldspar and the rest is ferromagnesian minerals.

Marble
(Metamorphic)

Metamorphic
Crystalline, fine to coarse grained.
Mineral comp.: Calcite or Dolomite

Magnetite

Streak Color: Black
Hardness: Harder than glass
Cleavage: Absent

Steel Gray to dull black, H=6; metallic luster, MAGNETIC

Amphibole
(Metamorphic)

Coarse Grained= large grains that can be seen unaided.
Layered foliation.
More than 90 percent Amphiboles

Siltstone
(Sedimentary)

Fine Grained
Composed of quartz and clay minerals

Calcite
(Sedimentary)

Streak: White/light gray
Softer than glass, but harder than fingernail.
Cleavage: Present

Colorless to white.
H=2.5, C=3 directions NOT at 90.
(rhombic)
Glassy luster, white streak
*<b>Reaction to HCl</b>*

Bituminous Coal
(Sedimentary)

H: , S.G. 1.1 - 1.4,
Streak: Black
Color: dark brown to black in color and commonly banded, or layered

Carbonaceous- Glassy to blocky.
Composition: carbon (organic)

Gneiss
(Metamorphic)

H: 7, S.G. 2.6 - 2.9
Streak: white
Luster: Dull
Color: Black, Brown, Pink, Red, White

Banded foliation.
Coarse Grained
Mineral composition: Quartz, feldspar, amphibole/hornblende

Obsidian
(Igneous)

H: 5-5.5, S.G. 2.6-2.7, Streak: white
Glassy
Mafic
Color: Black, Blue, Brown, Green,
Naturally occurring volcanic glass formed as an extrusive igneous rock. It is produced when felsic lava extruded from a volcano cools rapidly with minimum crystal growth

Sedimentary

rock that has formed from sediment deposited by water or air.

Metamorphic

rock that has undergone transformation by heat, pressure, or other natural causes

Igneous

Rocks that form from the cooling of a melt.

What are the 4 ways a rock can change when it undergoes metamorphism?

1) Change in rock density
2) change in mineral size
3) change in mineral grain orientation
4) change mineralogy of rock

What are the four steps to making a Sedimentary Rock?

1. Weathering
2. Transport
3. Deposition
4. Lithification/cementation

Special Properties

-Smell
-Taste
-Acid Reaction
-Magnetism
-Feel
-Flexibility
-Elasticity
-Conchoidal Fracture
-Striations
-High Density

Rock texture describes:

1. Grain size
2. Grain shape
3. Grain orientation

Streak

the color of a mineral's powder

Why is color less important than streak?

Important when identifying a mineral because minerals can be all sorts of colors but all specimens of that mineral share the same streak color. This a more reliable source when identifying minerals.

Gabbro
(Igneous)

MAFIC
Origin: Intrusive
Grain size: coarse grained
Texture: Phaneritic

Pegmatitic Texture

-VERY LARGE crystals (wider than pinky finger)
-INTRUSIVE texture

Phaneritic Texture

-Coarse Grained (Mineral grains are large enough to see with unaided eye.)
-INTRUSIVE texture

Aphanitic Texture

-Fine Grained (Minerals grains are too SMALL to be seen with unaided eye).

-EXTRUSIVE texture

Porphyritic Texture

-Often a mixture of fine and coarse grained.
(2 different (at least) sized mineral grains.)

-2 RATES OF COOLING

-Intrusive/Extrusive Texture

Glassy Texture

-No mineral grains to be seen.
-EXTRUSIVE texture

Vesicular Texture ("frothy")

-Lava contained large amounts of gas (like CO2 ).
-EXTRUSIVE texture

Fragmental Texture (Pyroclastic)

-Rock is made of fragments of volcanic glass, mineral crystals, or lithic (rock) fragments. Much of the rock is ash.
-EXTRUSIVE texture

What are 5 things a Mineral must be?

1. Solid
2. Naturally Occurring
3. Inorganic (usually)
4. Definite, but not fixed, Chemical Composition
5.Ordered Internal Arrangement (Crystalline Structure)

Color

The color that you see when you observe the sample.

Luster

A mineral's appearance when light is reflecting off its surface.
(Ex: Metallic, Non-Metallic- glassy, pearly, dull, fibrous)

Specific Gravity

A unitless number that shows a ratio of the density of a substance in relation to the density of water.

Striations

Look like small parallel lines etched into a minerals face.

Detrital Sedimentary Rocks

rocks that form from the accumulation of materials that originate and are transported as solid particles derived from both mechanical and chemical weathering

Galena

Color: Dark gray
Luster: metallic
Streak: Dark gray
Hardness: 3
Cleavage: 3 directions @ 90.

Is DIORITE igneous, sedimentary, or metamorphic?

Igneous

organic sedimentary rock

Sedimentary rock that forms from the remains of plants or animals

What igneous texture best describes Gabbro?

Phaneritic

Is PHYLLITE igneous, sedimentary or metamorphic?

Metamorphic

What is calcite made of (majority)?

fossiliferous limestone

Intermediate

SiO2 content: Intermediate
Viscosity: High/Medium
Temperature: ~800 C

What are the 4 compositional varieties (Igneous groups)?

Felsic, Intermediate, Mafic, Ultramafic

Is CALCITE igneous, sedimentary, or metamorphic?

Sedimentary

What tectonic environment did Gabbro form in?

Rift/Hot spot

The three agents that cause Metamorphism:

1) Heat
2) Pressure
3) Chemically Active Fluids (H20), CO2)

Felsic

SiO2 content: High
Viscosity: High
Temperature: ~650 C

Anthracite Coal

Non-Foliated Metamorphic Rock.

Texture: Carbonaceous- glassy/greasy

Mineral Composition: Carbon (organic in origin)

Is ANTHRACITE COAL igneous, sedimentary, or metamorphic?

Metamorphic

Ultramafic

Will not see in lab. Rare on Earth's Surface.
Even less silica than mafic.

Breccia

Sedimentary rock
Texture: Coarse Grained. (gravel size)

consisting of angular fragments; or rock broken into angular fragments by faulting

What texture does Obsidian have?

Glassy texture

Granitic rocks come from what tectonic environment?

subduction zones

Mafic

SiO2 content: LOW
Viscosity: LOW
Temperature: ~1100 C

Is MARBLE igneous, sedimentary, or metamorphic?

metamorphic

chemical sedimentary rock

Sedimentary rock that forms when minerals precipitate from a solution or settle from a suspension

Magma

Molten rock BENEATH the earth's surface

Lava

Magma that reaches Earth's SURFACE

Sedimentary rock textures

Fine grained
Medium grained
Coarse grained

What is the definition of a mineral?

-Solid
-Naturally occurring
-Inorganic (usually)
-Definite, but not fixed, chemical composition
-Ordered crystalline structure