Rilandite

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.

How a mineral resists breaking, bending, or crushing. Brittle snaps cleanly, malleable hammers into sheets, sectile slices like soft metal.

The shape of a broken surface that doesn't follow cleavage — conchoidal (curved, like broken glass), uneven, hackly, or splintery.

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

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