Mineralogy and Petrology – Engr. Emily

Mineralogy

Science of minerals: their properties, classification, occurrence, and identification.

Crystallography

Study of crystal structures, atomic arrangements, and how these relate to material properties.

Polymorphs

Minerals with the same chemical composition but different crystal structures (e.g., diamond vs graphite).

Form (crystal form)

Group of crystal faces with the same relation to the crystal’s symmetry elements.

Habit (crystal habit)

Outward appearance of a crystal or aggregate; influenced by growth conditions.

Amorphous solid

Solid lacking ordered crystal structure (e.g., glass, obsidian).

Crystalline solid

Solid with a well-ordered, repeating atomic arrangement.

Anisotropic

Exhibiting direction-dependent properties (e.g., hardness, refractive index).

Isotropic

Properties are the same in all directions.

Crystal

Solid having a regularly repeating Arrangement of atoms. Crystalline Structure.

Crystal lattice

3D array of points representing the periodic arrangement of atoms in a crystal.

Unit cell

Smallest repeating unit that fully describes the crystal structure. Fundamental elementary pattern, “building blocks”.

Primitive lattice (P)

Lattice with atoms only at the corners of the unit cell.

Body-centered

Lattice with atoms at the corners and in the body center.

Face-centered

Lattice with atoms at the corners and at the centers of each face.

Base-centered

Lattice with atoms at the corners and at the centers of the base faces (top and bottom)

Interfacial/Interaxial angles

Angles between adjacent crystal faces.

Lattice constants

Edge lengths along the principal axes of a crystal lattice.

Crystallographic Axes

Set of reference axes in a crystal that are used to describe the crystal systems.

Euler’s Formula

# of faces + # of solid angle = # of edges + 2

Crystal System

Refers to the geometry of crystal structuree. It is described by crystallographic axes.

Isometric/Cubic

System where three axes are equal; high symmetry (example: halite).

Tetragonal

Three axes, all perpendicular; two axes equal in length, one distinct. (Ex. Apophyllite)

Orthorhombic

Three mutually perpendicular axes of different lengths.

Trigonal/Rhombohedral

Three axes of equal length. No perpendicular lengths (Ex. Calcite)

Monoclinic

Three axes, two not perpendicular; one angle non-90°.

Hexagonal

Four axes with three in one plane 120° apart; one perpendicular axis to the other 3 lengths.

Bravais lattices

Distinct lattice types: Primitive (P), Body-centered (I), Face-centered (F), and others (C, etc.).

Crystal forms

Closed vs open forms; the set of crystal faces that define a form.

Symmetry element

Geometric feature (plane, line, or axis) used to describe symmetry in crystals.

Translational Symmetry

Symmetry accompanying the translation or movement of a plane or unit cell without rotation.

Glide Planes

Symmetry that involves translation parallel to the glide planes, followed by reflection across the glide planes.

Screw Axis

Translation parallel to the screw axis, followed by rotation about the screw axis.

32 Point Groups

Classification of crystal symmetry excluding translational symmetry.

Space group

Combination of crystal symmetry operations including translations; 230 known space groups.

Axis of Symmetry

Line about which the crystal may be rotated so as to show the same view of the crystal more than once per rotation

Diad

2 fold axis; when rotating the same face/view occurs 2 times

Triad

3 fold axis; when rotating the same face/view occurs 3 times

Tetrad

4 fold axis; when rotating the same face/view occurs 4 times

Hexad

6 fold axis; when rotating the same face/view occurs 6 times

Schoenflies Notation

Usually used in spectroscopy. Enough to describe symmetry of molecule.

Hermann-Maguin Notation (International Notation)

Can describe the symmetry of elements in point groups, plane groups, and space groups of crystal lattice.

Crystal growth

Expansion of a crystal as atoms/ions attach to its surfaces.

Nucleation

Formation of a stable seed (nucleus) from which crystals grow.

Heterogeneous nucleation

Nucleation aided by surfaces, impurities, or artificial seeds.

Slow cooling method

Crystallization by cooling a saturated solution slowly; solubility decreases with temperature.

Slow evaporation method

Crystallization by gradual solvent removal to precipitate solute.

Temperature gradient method

Crystallization driven by transport from hot to cold regions, causing deposition.

Critical nucleus radius

Minimum stable size a nucleus must reach to continue growth.

Crystallization

Process through which atoms, molecules, or ios arrange themselves in a repeating pattern

Supercooling

the cooling of a liquid below its equilibrium freezing or crystallization temperature without the immediate formation of solid crystals.

Euhedral

Crystal faces are well-formed and clearly developed.

Subhedral

Crystal faces are partially developed; some faces are well-formed.

Anhedral

Crystal with no well-formed crystal faces.

Crystal habits

Common shapes crystals can take, e.g., acicular, tabular, platy, prismatic.

Prismatic

Long and slender, with well-formed prism faces (Beryl, Tourmaline)

Tabular

Crystals are flat and plate-like, resembling a tablet (Barite, Apophyllite)

Equant

Crystals have roughly equal dimensions in all directions, often forming blocky shapes (Garnet, Halite)

Acicular

Crystals are very thin, slender, and needle-like (Natrotile, Rutile)

Fibrous

Crystals appear as fine threads or fibers (Chrysotile, Asbestos)

Capillary

Crystals are extremely thin and hair-like, often finer than fibrous types. (Millerite)

Bladed

Crystals are flat and elongated, shaped like knife blades (Kyanite)

Columnar

Crystals are thick and vertical, resembling pillars or columns; tourmaline, pyroxene, and augite

Lenticular

Crystals are lens-shaped and rounded, like in siderite and hematite

Filiform

Crystals grow as flexible wire-like threads, typical of native copper and native silver

Dendritic habit

Arborescent, tree-like crystal growth with branched forms, like pyrolusite, manganese oxides, and silver.

Reticulated habit

Lattice-like, networked crystal aggregation

Drusy habit

Surface covered with a dense layer of minute crystals.

Mammillary habit

Large, rounded masses formed by radiating growth.

Radiating

Crystals grow outward from a central point, found in pyrite, natrolite, and wavellite

Roseiform

Crystals cluster in a flower-like shape, as seen in barite (desert rose) and gypsum rose

Botryoidal

Crystals form rounded, grape-like masses, common in malachite, hematite, and smithsonite.

Reniform

Crystals form kidney-shaped, curved surfaces, typical of hematite and goethite.

Globular

Crystals form spherical clusters, seen in prehnite and smithsonite.These clusters often resemble small balls or globes.

Oolitic

Rock made of tiny, spherical grains like fish eggs, common in limestone and iron-rich sediments.

Pisolitic

Like oolitic but with larger rounded grains, found in bauxite and limonite

Stalactitic

Hanging, icicle-like mineral growths, formed by calcite, aragonite, and malachite in caves

Geode

Hollow rock cavities lined with inward-growing crystals like quartz, amethyst, and calcite

Massive

A dense, compact form with no visible crystals, typical of magnetite, chalcopyrite, and galena

Granular

Made up of small, equant interlocking crystals, seen in dolomite, olivine, and calcite.

Plumose

Crystals show a feather-like or plume-like pattern, often radiating in delicate, curved arrangements

Lamellar

Crystals form in stacked, sheet-like layers, as in graphite, hematite, or chlorite.

Foliated

Thin, flexible layers of crystals that peel easily, seen in micas like biotite and muscovite

Bonding (ionic)

Electrostatic attraction between oppositely charged ions; high melting points.

Bonding (covalent)

Electron sharing between atoms; common in nonmetals.

Bonding (metallic)

Delocalized electrons bonding metal ions; gives metallic conductivity.

Native elements

Minerals consisting of a single element in pure form (e.g., Cu, Au, Ag).

Sulfides

Minerals composed of sulfur bonded to a metal cation (e.g., pyrite, galena).

Sulfates

Minerals with sulfate (SO4)2- groups bonded to metals.

Oxides

Metal cations bonded with oxygen; hard, dense minerals (e.g., hematite, magnetite).

Hydroxides

Minerals with hydroxide groups (OH-); often hydrated oxide forms.

Halides

Minerals containing halogen ions (Cl-, F-, Br-), such as halite (NaCl).

Silicates

Most abundant group; SiO4 tetrahedra form various structures (nesosilicates to tectosilicates).

Carbonates

Minerals containing CO3 groups (e.g., calcite, dolomite).

Phosphates

Minerals with phosphate groups (e.g., apatite).

Nesosilicates (Olivine group)

Isolated SiO4 tetrahedra; olivine with Forsterite and Fayalite as endmembers.

Inosilicates (Pyroxene group)

Single/double chain silicates; includes pyroxenes like enstatite and augite.

Amphiboles (Double chain)

Inosilicate group (e.g., hornblende) with two chains; commonly hydrous.

Phyllosilicates (Micas)

Sheet silicates; forms mica group (Biotite, Muscovite).

Tectosilicates (Framework)

3D framework silicates; includes feldspars and quartz.