Metastibnite

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.

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.

The colour of a mineral's powder, drawn by scraping it across an unglazed porcelain plate. Far more consistent than surface colour.

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.

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

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

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 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.