Halite (sodium chloride) forms cubes — often with stepped "hopper" faces — and breaks into smaller cubes along three perfect cleavages at right angles. It is soft, light, and salty: a touch of the tongue to a fresh corner is diagnostic and, uniquely in this library, officially sanctioned. Found in evaporite beds and playa crusts.
Field identification workflow
- Look for cubes — growth faces, cleavage faces, or the stepped "hopper" depressions that record fast growth at a brine surface.
- Break a corner: three perfect cleavages at right angles yield smaller cubes, every time.
- Check hardness (2–2.5): a fingernail just scratches it.
- Apply the approved taste test — one clean corner, briefly. Salty is halite; bitter is sylvite; if you are unsure whether the specimen is safe to taste, you have skipped a step.