Athabascaite

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.

Resistance to being scratched, ranked on the Mohs scale from 1 (talc, marked by a fingernail) to 10 (diamond, scratches everything below it). The classic field test.

How the mineral's surface reflects light — from metallic and glassy to silky, pearly, or dull. Often the first clue to identification in the field.

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.

A change of colour as a coloured anisotropic mineral is rotated under plane-polarised light. Tourmaline and cordierite are textbook examples.

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 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.

How the mineral glows under short- and long-wave ultraviolet lamps. Some species fluoresce in spectacular colours invisible to the naked eye.

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.

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

The overall shape and habit a mineral tends to grow into — cubes, prisms, plates, fibres, druses, masses.

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.