Geo Test I

What is mineral luster?

How light reflects from a mineral's surface.

What are the two major categories of luster?

Metallic and nonmetallic.

What is hardness?

A mineral's resistance to scratching.

What scale measures mineral hardness?

The Mohs hardness scale.

What is cleavage?

The tendency of a mineral to break along specific planes of weakness.

What is fracture?

Breaking that does not occur along predictable cleavage planes.

What is streak?

The color of a mineral's powdered form.

What is specific gravity?

The density of a mineral compared with the density of water.

What is crystal habit?

The characteristic shape or appearance of a mineral crystal.

What does prismatic mean?

A crystal habit with elongated, prism-like crystals.

What does tabular mean?

A flat, tablet-shaped crystal habit.

What does bladed mean?

A long, thin, blade-like crystal habit.

What does fibrous mean?

A habit consisting of thin, thread-like crystals.

What does acicular mean?

Needle-like crystals.

What does dendritic mean?

Branching, tree-like crystal growth.

What does massive mean?

A mineral with no visible crystal shape.

What does botryoidal mean?

A cluster of rounded, grape-like forms.

What does reniform mean?

Kidney-shaped mineral growth.

What does oolitic mean?

Composed of small, rounded, egg-like grains.

What does pisolitic mean?

Composed of larger, rounded grains than oolitic material.

What is a geode?

A hollow rock cavity lined with crystals.

What are valence electrons?

Electrons in an atom's outermost energy level.

What is ionization potential?

The energy required to remove an electron from an atom.

What is electronegativity?

An atom's ability to attract electrons in a chemical bond.

What is ionic radius?

The effective size of an ion.

What is a cation?

A positively charged ion.

What is an anion?

A negatively charged ion.

What is an ionic bond?

An attraction between oppositely charged ions.

What is a covalent bond?

A bond formed when atoms share electrons.

What is metallic bonding?

Bonding involving freely moving electrons among metal atoms.

What is van der Waals bonding?

A relatively weak attraction between atoms or molecules.

Which bond type generally has high electrical and thermal conductivity?

Metallic bonding.

Which bond type is generally associated with very hard minerals?

Covalent bonding.

Which bond type commonly produces brittle minerals with good cleavage?

Ionic bonding.

What is coordination number?

The number of nearest neighboring ions surrounding an ion.

What is coordination polyhedron?

The geometric shape formed by an ion's nearest neighbors.

What is bond strength?

The strength of a chemical bond, often estimated by dividing an ion's charge by its coordination number.

What is the bond-strength equation?

Bond strength = ionic charge ÷ coordination number.

What is the radius-ratio rule used for?

Predicting the coordination number of an ion based on the relative sizes of the ions.

What happens when a cation is too large or too small for a coordination site?

The structure may become unstable or adopt a different coordination number.

What is Pauling's First Rule?

The coordination number of a cation is determined by the relative sizes of the cation and anions.

What is Pauling's Second Rule?

The total strength of bonds entering an anion should balance the anion's charge.

What is Pauling's Third Rule?

Shared edges and especially shared faces between coordination polyhedra reduce structural stability.

What is Pauling's Fourth Rule?

Different cations tend to avoid sharing the same anion when possible, especially if their charges and coordination numbers differ greatly.

What is Pauling's Fifth Rule?

The number of different structural components in a crystal tends to be limited.

What is a solid solution?

A mineral in which elements substitute for one another within an ordered crystal structure.

How is a solid solution different from a mechanical mixture?

The elements in a solid solution are chemically bonded and structurally ordered.

What is complete solid solution?

Substitution can occur across the entire compositional range between two end members.

Give an example of complete solid solution.

Forsterite-fayalite olivine: Mg₂SiO₄-Fe₂SiO₄.

What is limited solid solution?

Substitution occurs only over a restricted compositional range.

What is coupled substitution?

Two or more substitutions occur together to maintain charge balance.

What is omission solid solution?

Substitution involving the omission of ions or structural components while maintaining overall balance.

What is interstitial solid solution?

Smaller ions occupy spaces between the main ions in a crystal structure.

What are end members?

Ideal chemical compositions representing the components of a solid-solution series.

What are the three important feldspar end members?

Albite, anorthite, and orthoclase.

What is the general feldspar formula?

(Ca,Na,K)(Si,Al)₄O₈.

What are major elements?

Elements essential to a mineral's structure and basic properties.

What are minor elements?

Elements present in smaller amounts that commonly replace major elements.

What are trace elements?

Elements present in extremely small amounts that can sometimes affect color.

What is normalization of a mineral formula?

Adjusting calculated atomic proportions to a specific number of oxygen atoms or another structural basis.

What is the first step when converting oxide weight percentages into a mineral formula?

Convert each oxide weight percentage into moles by dividing by its molecular weight.

Why must oxide weight percentages be converted to mole values?

Mineral formulas are based on atomic proportions rather than mass percentages.

What is the formula of forsterite?

Mg₂SiO₄.

What is the formula of fayalite?

Fe₂SiO₄.

What mineral group do forsterite and fayalite belong to?

The olivine group.

What is the general olivine formula?

(Mg,Fe,Mn)SiO₄.

What is the crystal system of olivine?

Orthorhombic.

What is the structure of olivine?

Isolated SiO₄ tetrahedra linked by Mg²⁺, Fe²⁺, or other cations in octahedral coordination.

What color is Mg-rich olivine commonly?

Green or olive-green.

What color is Fe-rich olivine commonly?

Brown, yellow, or greenish-yellow.

What is the hardness of fayalite?

Approximately 6.5.

What type of fracture is common in olivine?

Conchoidal fracture.

What is peridot?

A gem-quality, transparent green variety of forsterite.

Which elements can substitute for Fe or Mg in olivine in minor amounts?

Calcium and nickel.

What is the formula of zircon?

ZrSiO₄.

What type of silicate structure does zircon contain?

Isolated SiO₄ tetrahedra.

Why is zircon important in geology?

It can contain uranium and lead, allowing radiometric dating of rocks.

What is the formula of quartz?

SiO₂.

What type of silicate structure does quartz have?

A three-dimensional framework of linked SiO₄ tetrahedra.

What are the two polymorphs of quartz emphasized for the exam?

Alpha quartz and beta quartz.

What is polymorphism?

The occurrence of the same chemical composition in different crystal structures.

Why does quartz have relatively little compositional variation?

It has a simple SiO₂ composition and a stable framework structure.

What is the formula of calcite?

CaCO₃

What polyatomic ion occurs in calcite?

The carbonate ion, CO₃²⁻.

Which mineral is a polymorph of calcite?

Aragonite.

What is the structural difference between calcite and aragonite?

They have the same chemical composition but different arrangements of ions and coordination environments.

What is the formula of corundum?

Al₂O₃

What is an important physical property of corundum?

It is very hard, with a Mohs hardness of approximately 9.

What is the formula of orthoclase?

KAlSi₃O₈

What is the formula of albite?

NaAlSi₃O₈

What is the formula of anorthite?

CaAl₂Si₂O₈

What are the major components of plagioclase?

Albite and anorthite.

What additional feldspar component may occur in plagioclase?

Orthoclase.

What are the three feldspar polymorph-related names emphasized in the exam?

Microcline, orthoclase, and sanidine.

What is the formula of periclase?

MgO

What mineral has a structure similar to halite?

Periclase.

What is the formula of spinel?

MgAl₂O₄

What type of structure does spinel have?

A structure containing both tetrahedral and octahedral coordination sites.

What is the formula of pyrite?

FeS₂

What is the formula of chalcopyrite?

CuFeS₂