Mineralogy and Crystallography Lecture 1

These vocabulary flashcards cover the fundamental definitions of minerals, their chemical abundance, symmetry elements, the six crystal systems, and physical properties used for identification from the Lecture 1 notes.

Mineral

A naturally occurring inorganic substance with a definite chemical composition and a regular internal structure.

Rock

A naturally occurring multi-granular aggregate of one or more minerals.

Elemental Composition of Earth's Crust

Mineral chemistry is a function of availability; $O + Si = 75\%$ by weight.

Cerium ($Ce$)

The most abundant Rare Earth Element (REE) in the average crust, found at $60-60\,ppm$.

Mirror planes

Imaginary planes through the center of a crystal that divide it into mirror image halves.

Rotation axes

Symmetry elements where the crystal is rotated $360^{\circ}$ around an axis; includes $1$-fold ($360^{\circ}$), $2$-fold ($180^{\circ}$), $3$-fold ($120^{\circ}$), $4$-fold ($90^{\circ}$), and $6$-fold ($60^{\circ}$).

Centre of symmetry

An inversion through the center to reach an equivalent point on the opposite side of the crystal.

Cubic crystal system

A system where all three axes are equal ($a_1 = a_2 = a_3$) and all angles are $90^{\circ}$.

Tetragonal crystal system

A system where two axes are equal and one is different ($a_1 = a_2 \neq c$), with all angles at $90^{\circ}$.

Orthorhombic crystal system

A system where all three axes are of different lengths ($a \neq b \neq c$) and all angles are $90^{\circ}$.

Hexagonal crystal system

A system defined by four axes ($a_1, a_2, a_3, c$) with horizontal angles of $120^{\circ}$ and vertical angles of $90^{\circ}$.

Monoclinic crystal system

A system where all three axes are of different lengths ($a \neq b \neq c$) and one angle is not at $90^{\circ}$.

Triclinic crystal system

A system where all three axes are of different lengths ($a \neq b \neq c$) and none of the angles are at $90^{\circ}$.

Lustre

The way light interacts with the surfaces of a mineral, described as metallic, sub-metallic, or non-metallic (vitreous, adamantine, greasy, silky, pearly, dull, pitchy, or resinous).

Hardness

The resistance of a mineral to abrasion, measured on the Mohs scale from $1$ (Talc) to $10$ (Diamond).

Cleavage

The tendency of a mineral to break along flat planar surfaces, determined by the structure of the crystal lattice.

Crystal form/habit

The characteristic external shape of a crystal or groups of crystals, determined as the crystal grows.

Twinning

The symmetrical intergrowth of two or more crystals of the same substance, which can be contact, penetrated, or multiple.

Unit cell

The smallest repeated unit in a crystal lattice.

Miller index

A system used to classify crystal planes based on how atoms are arranged in the structure.