Igneous Rocks and Minerals - GEOL 101

Minerals are

building blocks of rocks

How are chemical compounds formed?

by combining two or more elements in an orderly arrangement of atoms

Formation of a mineral is controlled

by the electrical charge of an ion (atom) and by its 'effective diameter' when fitting with other ions.

Where do minerals occur?

chemical groups corresponding to the tendency of metal atoms to combine with reactive elements O, C, S, P, F, Cl, etc

what does gabbro consist of

consist of pyroxene and calcium-rich plagioclase

Copper mine

copper oxides near top; copper sulfides at depth- formed as intrusion

What is gabbro?

crystallized version of basalt (Intrusive equivalent of basalt)

Examples of a polymorph

diamond and graphite

Amphibole group

double chain structures

What is the force that allows atoms to bond together

electrical force

What do metal-enriched residual fluids concentrate

elements not used by early crystallizing minerals in a melt; a process of enrichment.

What are three common silicate minerals?

feldspar, quartz, and mica

iron mine

iron oxides layered deposit- deposited as layers

what is basalt composed of?

mainly of pyroxene and plagioclase feldspar

Mica structure

sheets

What Comprises most rock-forming minerals?

silicates

What is the most important mineral group?

silicates

What are most rocks that we see made out of?

silicon, oxygen and metal atoms

Pyroxene group

single chain structures

Characteristics of quartz

Hard and resistant to weathering Glassy fracture Often forms hexagonal crystals

Characteristics of granite?

- Deep Crust igneous rock - Rock with high silica content - Forms deep in continental crust - Coarse grained - High amounts of silica (SiO2) - Light-colored silicate minerals

Characteristics of basalt

- Fine grained - often glassy - Comprise the ocean floor and many volcanic islands

Where do gem crystals occur

Often occur within open pockets in rock

Characteristics of gabbro

- low silica rock - Coarse grained

Structure of Feldspar and Quartz:

3 d structure

Can a polymorph change?

A polymorph can change into another phase, such as diamond changing to graphite when raised from great depth

Definition of a rock

A solid aggregate of minerals

How many rock forming minerals have been named?

Although nearly 5000 have been named, only a few dozen are common

Structure of an atom

Atom contains a nucleus, consisting of protons (+ charges) and neutrons (no charges), surrounded by electrons (- charge) Electron energy levels are called shells

How do atoms form ions?

Atoms gain or lose valence electrons to form ions

composition of mantle rock

Composition high in magnesium and iron Composed entirely of ferromagnesian silicates Composed of silicate minerals, mostly olivine (note the basalt; mantle rock brought out up by rising magma in volcano)

What allows minerals to precipitate from liquid

Cooling of magma

Changing magma composition

Crystallization of high temperature minerals (olivine, etc.) reduces concentration of some elements, changing composition and leading to different minerals crystalizing during magma cooling.

Process of crystallization

During crystallization, the composition of the magma changes, following the rule of continual rejection of ions by growing crystals, resulting in the greater consumption and depletion of some ions and enrichment in the magma of other ions, a process that leaves a residue rich in other ions. This leads to enrichment of rare elements in the magma.

Characteristics of mica

Excellent cleavage in one direction Produces the "glimmering" brilliance often seen in wet sand

Cleavage on feldspars

Exhibit two directions of perfect cleavage at 90 degrees

Crystal form

External expression of a mineral's internal structure. Very characteristic, but often not developed due to limited space and/or rapid cooling

Characteristics of olivine

High temperature mineral; not stable at lower temperatures Dissolves and goes back into melt as magma cools

What are the building blocks of minerals?

Ions: electically charged atom or group of atoms

Examples of silicate structures:

Isolated tetrahedra Ring structures Chain structure (single and double) Sheet or layered structures 3-dimensional structures

How do minerals crystallize?

Minerals crystallize in a systematic fashion based on their melting points

Polymorphs

Minerals with the same composition but different crystalline structures

Definition of a mineral:

Naturally occurring inorganic solid Ordered internal molecular structure Definite chemical composition

Most common feldspars

Orthoclase (potassium feldspar) and Plagioclase (sodium and calcium feldspar) are the two most common members

Characteristics of diorite

Plutonic equivalent of andesite Coarse grained

Ionized

Process of atoms giving up or receiving valence electrons, creating an electrical charge on the atom

result of changing magma composition

Result is change from basaltic, to andesitic, to granitic composition of magma, as metals (Fe,Mg) are depleted and silicon (Si) is enriched. Thus, the rocks have different mineral composition.

Igneous Rocks

Rocks that form by crystallization from or cooling of magma.

what does gabbro make up?

Significant % of the oceanic crust

How are silicate structures formed?

Single tetrahedra are linked together to form several silicate structures

Rock forming minerals are

The common minerals that make up most of the rocks of Earth's crust

Abundance of silicates

Very abundant due to large % of silicon and oxygen in Earth's crust Silicon-oxygen tetrahedron Fundamental building block: Four oxygen ions surrounding a much smaller silicon ion

Characteristics of andesite

Volcanic origin Fine grained

What is an ion?

an atom with an electrical charge, produced by losing or gaining an electron. It is the name of an atom that can bind with another atom to form a molecule, or in this case, a mineral.

ionic compounds consist of

an orderly arrangement of oppositely charged ions

What is the most common extrusive igneous rock?

basalt

Chemical compounds commonly have atoms bonded by

both ionic and covalent bonds

Examples of minerals

gemtones, birthstones,

density of basalt compared to granite

higher density of granite rocks

ionized atoms

imbalance between electrons and protons

when do Ore deposits form

in late stages of igneous intrusions, from metal-enriched residual fluids.

andesite and diorite are both

intermediate rocks

Is granite extrusive or intrusive?

intrusive

Dark colored minerals commonly have

iron (Fe) and magnesium (Mg)

the most common rock mined, crushed, and used for aggregate fill and roads

limestone

Rock forming minerals are composed of

mainly of the 8 elements (O, Si, metals) that compose over 98% of the continental crust

What rock has the lowest silica

mantle rock

What is the First mineral to crystallize from cooling magma

olivine

Only common silicate composed entirely of oxygen and silicon is

quartz

How is basalt formed?

the partial melting of liquid rock

How do igneous rocks form?

when molten rock (magma, lava) cools and solidifies