Gachingite

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

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.

Whether an opaque mineral changes brightness or hue as the stage is rotated under crossed polarisers in reflected light. A key ore-mineral test.

A visible change in reflectance as an opaque mineral is rotated under plane-polarised reflected light. Diagnostic for ore minerals.

A general label for how an opaque mineral responds to polarised reflected light, summarising bireflectance and anisotropism together.

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

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.