Petewilliamsite

The kinds of rock environments where the mineral typically forms — igneous, metamorphic, hydrothermal, sedimentary, pegmatitic, and so on.

The place where the mineral was first found and described — by convention, the reference point for the species.

Whether and how much light passes through a mineral, from transparent (you can see through it) to translucent, then opaque.

The hue of the mineral itself. Often unreliable for identification — many species occur in several colours depending on trace impurities or radiation damage.

Mass per unit volume, in grams per cubic centimetre. A useful sorting tool: barite is twice as dense as quartz at the same size.

The colour seen through a polarising microscope — often unlike the hand-specimen colour, because section thickness and orientation both matter.

Coloured glints from inside an opaque mineral, seen when light reaches translucent zones beneath the polished surface.

The percentage of incident light reflected by a polished surface, measured at standard wavelengths. The defining property of ore microscopy.

One of seven geometric families that describe a mineral's atomic symmetry: isometric (cubic), tetragonal, hexagonal, trigonal, orthorhombic, monoclinic, triclinic. Two non-crystalline classes — amorphous and icosahedral — also appear.

The full symmetry description of a crystal's repeating atomic pattern — 230 distinct groups, written in Hermann–Mauguin notation (e.g. P6₃/mmc).

The lengths of the unit-cell edges (a, b, c) in ångströms — the smallest repeating box of atoms that builds the crystal.

The angles (α, β, γ) between unit-cell edges, in degrees. Cubic crystals have 90°/90°/90°; triclinic crystals can take any combination.

Edge-length ratios of the unit cell, normalised so b = 1. Lets you compare related species without quoting absolute ångström values.

Volume of the unit cell in cubic ångströms (ų). Reflects how tightly the atoms are packed for a given chemistry.

The number of formula units contained in a single unit cell.

The crystal habit observed at the type locality — the place where the mineral was first described.

Chemical elements that make up the mineral's ideal formula, listed by atomic symbol with their share of the total mass.

Minor or trace elements outside the ideal formula but commonly detected in natural specimens. Often the cause of colour variation.