Mineralogy 2026 Midterm Chapters 1-10

Pain and suffering, chapter one through whatever we finish before Monday. I hate my life.

Mineral

a naturally occurring solid with a highly ordered

atomic arrangement and a definite (but not fixed) chemical

composition. It is formed by inorganic processes.

A Mineral has to be….

Naturally occurring, homogenous solid, have a definite chemical composition, a highly ordered atomic arrangement, and formed by inorganic processes

Properties primarily controlled by atomic

arrangement and bonding

hardness, habit, tenacity, magnetism, cleavage, density

Hardness

Related to the atomic structure of the mineral and its weakest bonds

Tenacity

Resistance to breaking, or “cohesiveness”

Cleavage

Breaking along planes of weakness

Fracture

broken surface is irregular

Habit

The external shape (appearance) of a mineral

Reflects internal structure

Habit - Fibrous

Long, slender fibers

Habit - acicular

elongate, needle-like

Habit - Bladed

elongate, slender

Habit - columnar

shaped like a column

Habit - tabular

shaped like a book

Habit - blocky

block like

Habit - radiating

a group of radiating crystals from a central point

Magnetism

Controlled by electron spin

Minerals can be non-______, or weakly to strongly _______

Density

_____= mass/volume (in g/cm3 or kg/m3)

Depends on composition, structure, temperature, and pressure

Specific Gravity

Density of mineral / Density of water = __________

Color of Minerals

Not always a reliable property, caused by absorption of various wavelengths of life, what isn’t absorbed is what we see

Chemical Bonding

The power of bonds derives from electrons and how

they are shared in the filling of outer orbitals; Negative and positive particles attract each other

Van der Waals forces

Between molecules, e.g., layers of graphite, talc

• Weak electrostatic attraction

• Due to short-term polarization between sheets

• Very soft

• High compressibility, thermal expansion

Steno’s Law

“The angles between equivalent faces of crystals of the same substance,

measured at the same temperature, are constant”

Motif

the fundamental part of a symmetric design that, when

repeated, creates the whole pattern. It has all the symmetry of the entire crystal.

Point symmetry

Repetition of patterns due to rotation, reflection or inversion (e.g., crystal faces)

Repeats something a specific(discrete) number of times about a central point

Returns a motif to its original position after the operations

Translational (space) symmetry

Repetition of patterns due to __________

Repeats something an infinite number of times to fill space (no voids!)

Does not return to original position: could go on forever!

Lattice

continuous repeating pattern of points in a plane

(2D). Could extend to infinity by translation. One point = a node

Unit Mesh

The smallest, fundamentally different shapes in 2D that a lattice can consist of

Unit Cell

a 3D unit mesh. It has all of the symmetry of the main structure

2D Lattice - Oblique

a ≠ b, γ ≠ 90°

2D Lattice - Rectangle (p)

a ≠ b, γ = 90°

2D Lattice - Rectangle ( c )

a ≠ b, γ = 90, Notice that this lattice has diamond shapes

2D Lattice - Rhombus

a = b, γ = 120°, Notice that this lattice has hexagon shapes

2D Lattice - Square

a = b, γ = 90

Bravais Lattices

14 unique ________ that all minerals can be classified into; divided amongst the six crystal systems based upon the shape of the unit cell

Operation (about a point)

some act that reproduces the motif to create the pattern. Includes translation, as well as reflection, rotation, inversion.

Element (about a point)

an operation located at a particular point in space

10 Unique Point Groups -2D

1, 2(i), 3, 4, 6, m, 2mm, 3m, 4mm, 6mm

3D Symmetry - Inversion

take every point and pass it through the center of the shape; Notation = i. Also called “center of symmetry”

Isometric System

This literally means “equal measure” and refers to the equal length of the crystal axes.

■ Highest symmetry: All have four 3-fold or four 3-bar roto inversion symmetry elements.

Hexagonal System

Either have a single 3- or 6- fold rotation depending on if they are ______ or _______-trigonal

Three horizontal axes of same length (a1-a3) at 120° and a c axis perpendicular to them

Tetragonal System

Have one 4-fold axis (or 4-bar) (but beware! Some isometric minerals also have 4-fold axes!!)

Two axes with equal length (a1-a2) and a 3rd axis (c) mutually perpendicular

Orthorhombic System

All the axes are perpendicular, but they are all different lengths. Every axis has symmetry, either 2-fold or m

Monoclinic

____= one axis of symmetry (either a 2-fold or a mirror)

a and b perpendicular

b and c perpendicular

a and c oblique

Triclinic

Lowest symmetry group. The only options are 1 or 1-bar

All axes different lengths

All axes are at oblique angles to each other (none perpendicular)

Crystal Faces

The frequency with which a given ____ in a crystal is observed is proportional to the density of lattice nodes along that plane (Bravais Law)

Crystal Morphology

Because faces have a direct relationship to the internal structure, they must have a direct and consistent angular relationship to each other

Form

A set of symmetrically equivalent faces. These will have identical atomic structure

Open form

does not enclose space

Closed Form

They enclose a volume of space.

Crystals with one form must be closed.

General form

the form for which the crystal class is named; the max. number of faces of any form in its crystal class

Special Form

any form which is not a general form

Crystal Nucleation

First step in crystal growth; formation of a crystal nucleus from which a crystal will grow.

Heterogeneous nucleation

nucleation on a pre-existing solid material e.g. phenocryst, minute smaller crystals, xenoliths.

Homogeneous nucleation

random thermal fluctuations trigger _________. Undercooling of magmas and supersaturation of magmas is required.

Twinning

Two general types of twin styles - contact and penetration

Form as a result of an error during crystallization

Twinning Laws

An intergrowth of two or more orientations of the same mineral with a crystallographic relationship. Mistakes during crystallization, predominantly thought to be nucleation error

Coordination Number

number of nearest neighbors (# of anions surrounding a cation).

R C / R A

Metallic bonding

usually close packing, cubic or hexagonal, as atoms are generally identical size.

Ionic bonding

approaches close packing but packing also depends on radius ratio of

cation to anion

Covalent bonding

reflects the directional nature of the bond; generally 4-fold CN

Pauling’s 1st Rule: The Coordination Principle

Around every cation, a coordination polyhedron of anions forms.

The cation-anion distance = Σ radii

Use R C/R A (radius ratio) to determine the coordination number of the cation

Pauling’s 2nd Rule: Electrostatic Valency Principle

In a stable crystal structure, the total strength of the valency bonds that reach the cation from all the neighboring anions is equal to the charge of the cation (essentially sharing with nearest neighbors to balance charge).

Pauling’s 3rd Rule: Sharing of polyhedral elements I

The sharing of edges (image B) and faces (image C) of adjacent polyhedral tend to decrease the stability of an ionic structure.

Highly charged cations, such as Si4+ use corner sharing (image A)

Pauling’s 4th Rule: Sharing of Polyhedral Elements II

In a crystal with different cations, those of large valence and small CN tend to not

share polyhedral elements (An extension of Rule 3)

Pauling’s 5th Rule: Principle of Parsimony

The number of different kinds of constituents in a crystal tends to be small:

simpler is better!

Precipitation from Fluid

These minerals are typically soluble in water

A decrease in temperature may lead to oversaturation and _______of the minerals

Evaporation of water may also lead to oversaturation and _______

Basaltic magma

high in Fe, Mg, and Ca It ranges in temperature from about 1000°C to 1200°C

Andesitic magma

moderate amounts of Fe, Mg, Ca with higher Si, Na, K, with a temperature range from about 800°C to 1000°C

Rhyolitic magma

high in K and Na, low in Fe, Mg, and Ca. It occurs in the temperature range of

about 650°C to 800°C

Solidus

A boundary where the rock/mineral is solid below the boundary, and starts to melt above the boundary

Metamorphism

change in mineral assemblage and texture of a rock in response to a change in the ambient physical conditions

Tridymite

Formation temperature of ______, 870°C, is well within the normal magmatic temperature range, however tridymite generally forms in silica-rich rocks at lower temperature and must therefore form meta-stably in most cases.

Cristobalite

No terrestrial magma gets as hot as the equilibrium formation temperature of ________(1470C). Since it is common in cavities in low-temperature volcanic rocks like obsidian, as well as some sedimentary settings, it must form also metastably.

Coesite

formed by deep burial of crust, due to

collisional processes

Solid solution

Combine two end member compositions to create a continuous range in mineral composition

Liquidus

A boundary where the rock/mineral is liquid above the boundary, and starts to crystallize below the boundary

Relief

the amount by which a mineral stands out from it’s surroundings

Isotropic

properties are the same in all directions

Anisotropic

properties change as a function of direction

double refraction

The splitting of a light beam into two perpendicular polarized rays