Sci 405 - Geology Midterms

Naturally occurring

Generally inorganic

Solid substance

Orderly crystalline structure

Definite chemical composition

Geologic Definition of Mineral:

Rock

A solid mass of minerals or mineral-like matter that occurs naturally

Atom

Smallest particles of matter that cannot be chemically split

principal shells

Electrons exist as a cloud of negative charges surrounding the nucleus of protons and neutrons, occurring in regions called

Atomic number

The number of protons in the nucleus of an atom

Octet rule

Atoms tend to gain, lose, or share electrons until they are surrounded by eight valence electrons

Ionic bond

the attraction of oppositely charged ions to one another

Covalent bonding

Atoms share one or more valence electrons

Metallic bonding

Valence electrons are free to migrate among atoms

Geodes

Minerals can precipitate from slowly moving groundwater filling fractures and voids.

Luster

Color

Ability to transmit light

Streak

Crystal shape

Primary diagnostic properties of minerals:

Hardness

Cleavage

Fracture

Tenacity

Mineral strength properties of minerals:

Density

Specific gravity

Taste

Feel

Stinky streak

Magnetism

Doublerefraction

Effervescence

Other properties of minerals:

Luster

Appearance of a mineral in reflected light

MetallicNonmetallic

Two basic categories of luster:

Opaque

no light is transmitted

Translucent

light, but no image is transmitted

Transparent

light and an image are visible through the sample

Color

Generally unreliable for mineral identification

Streak

Color of a mineral in its powdered form

Crystal Shape, or Habit

Characteristic shape of a crystal or aggregate of crystals

Hardness

Resistance of a mineral to abrasion or scratching

1.talc

2. gypsum

3. calcite

4. fluorite

5. apatite

6. orthoclase

7. quartz

8. topaz

9. corundum

10. diamond

Mohs hardness scale softest to hardest:

Cleavage

Tendency to break (cleave) along planes of weak bonding

Fracture

Minerals with equally strong bonds have an absence of cleavage

Brittle

minerals (such as those with ionic bonds) will shatter into small pieces.

Malleable

minerals (such as those with metallic bonds) are easily hammered into different shapes.

Sectile

minerals, such as gypsum and talc, can be cut into thin shavings.

Elastic

minerals, such as the micas, will bend and snap back to their original shape.

Density

is defined as mass per unit volume

Specific gravity

The ratio of the weight of a mineral to the weight of an equal volume of water

Effervescence

Carbonates fizz in reaction to dilute hydrochloric acid

Magnetism

Magnets pick up magnetite, lodestone is a natural magnet

1. plagioclase feldspars

2. potassium feldspars

3. quartz

4. pyroxenes

5. amphiboles

6. micas

7. clays

8. nonsilicates

9. other silicates

Rock forming minerals:

Silicates

are the most common type of minerals (more than 800 known silicates).

Clay

is a general term used to describe a variety of complex fine-grained minerals that have sheet structure

lava

Magma at surface is called

volatiles

are dissolved gases in the melt that vaporize at surface pressure

crystallization

is the cooling of magma which results in the systematic arrangement of ions into orderly patterns.

plutonic or intrusive igneous rocks

Magma that crystallizes at depth forms

Granitic or felsic composition

Igneous composition that is composed of light-colored silicates

Basaltic or mafix composition

Igneous composition that contain at least 45% dark silicates and calcium-rich feldspar

Andesitic or intermediate composition

Igneous composition that contain 25% or more dark silicate minerals (amphibole, pyroxene, and biotite mica)

Ultramafic composition

Igneous composition that are rare composition of mostly olivine and pyroxene

Peridotite

is an example and the main constituent of the upper mantle.

Granitic magmas

have high silica content, are viscous (thick), and erupt at a lower temperature.

Basaltic magmas

have much lower silica content, more fluid like behavior, and erupt at a higher temperature.

Texture

describes the overall appearance of a rock based on the size, shape, and arrangement of mineral grains.

Aphanitic texture

Igneous texture that is the result of rapid rate of cooling forming microscopic crystals

Phaneritic texture

Igneous texture that is the result of slow rate of cooling forming visible crystals

Porphyritic texture

Igneous texture that forms large crystals (phenocrysts) are embedded in a matrix of smaller crystals (groundmass)

Vesicular texture

Igneous texture that contain voids left by gas bubbles in the lava

Glassy texture

Igneous texture where Ions are frozen in place before they can unite in an orderly crystalline structure

Pyroclastic texture

Igneous texture that forms from the consolidation of individual rock fragments ejected during explosive eruptions

Pegmatitic texture

Igneous texture that is exceptionally coarse-grained; form in late stages of crystallization of magmas (rocks are called pegmatites)

Granite

Coarse-grained, 10-20% quartz, roughly 50% potassium feldspar, Small amounts of dark silicates

Rhyolite

Extrusive equivalent of granite, composed of essentially of light-colored silicates

Obsidian

Dark-colored, glassy rock, forms when silica-rich lava cools quickly at Earth's surface, black to reddish-brown in color.

Pumice

Glassy textured rock with vesicular texture that forms when large amounts of gas escape from the lava

Andesite

Medium gray, fine-grained rock, usually porphyritic

Diorite

Intrusive equivalent of andesite, coarse-grained, have salt-and-pepper appearance.

Basalt

Very dark green to black, fine-grained rock, composed mostly of pyroxene and calcium-rich plagioclase feldspar

Gabbro

Intrusive equivalent of basalt, very dark green to black, composed mostly of pyroxene and calcium-rich plagioclase feldspar

Tuff

Most common pyroclastic rock

Welded tuff

Ash particles are hot enough to fuse together

Volcanic breccia

Composed of particles larger than ash. Includes streamlined lava blobs, broken blocks of vent walls, ash, and glass fragments

Geothermal gradient

temperatures in the upper crust increase about 25°C per kilometer

Decompression Melting

Melting occurs at higher temperatures with increasing depth (and increasing confining pressure).

Flux melting

Water and other volatiles act as salt does to melt ice causing rocks to melt at lower temperatures.

Bowen's Reaction Series

Minerals crystallize in a systematic fashion based on their melting points.

Crystal settling

Earlier-formed minerals are denser than the liquid portion of the magma and sink to the base of the magma chamber.

Magmatic differentiation

The formation of one or more secondary magmas from a single parent magma.

Assimilation

As magma migrates through the crust, it may incorporate some of the surrounding rock into the chamber, melting and changing the chemical composition.

Magma mixing

During the ascent of two chemically different magma bodies, the more buoyant mass may overtake the slower-rising body, merging them, and their melts mixing by convective flow.

pluton

is cooled, emplaced magma into preexisting rocks

Dike

a tabular, discordant pluton

Sill

a tabular, concordant pluton

Batholith

Largest intrusive body (>100 square km)

Stocks

smaller batholith (<100 square km)

Xenoliths

are suspended blocks of country rocks found in plutons

Laccoliths

Overinflated sills

Sedimentary rocks

are products of mechanical and chemical weathering

Detrital sedimentary rocks

form from sediments that have been weathered and transported

Shale

Silt- and clay-sized (fine-grained) particles, has fissility

Sandstone

Second most abundant sedimentary rock

Sorting

is the degree of similarity in particle size

Particle shape

varies from rounded to angular

Conglomerate

consists of rounded, gravel-sized sediments

Breccia

consists of angular, gravel-sized sediments

Chemical sedimentary rocks

form from precipitated material that was once in solution

Limestone

Most abundant chemical sedimentary rock

Biochemical limestone

originates from the shells of marine organisms

Coquina

is composed of cemented fragments of shell material

Chalk

is composed of the hard parts of microscopic marine organisms

Inorganic limestone

forms when chemical changes increase the calcium carbonate content of the water until it precipitates

Travertine

is a type of limestone found in caves

Oolitic limestone

is composed of small spherical grains called ooids

Dolostone

Similar to limestone but contains magnesium

Chert

Composed of microcrystalline quartz

Organic sedimentary rocks

form from the carbon-rich remains of organisms