Halite
NaCl · Cubic · also called rock salt
Halite is ordinary salt in mineral form. It is one of the very few minerals identified by taste, and the combination of cubic cleavage, low hardness, and water solubility leaves no real alternatives.
Properties
- Mohs hardness
- 2–2.5
- Streak
- white
- Lustre
- vitreous
- Colour
- Usually colourless or white; some deposits produce startling blue or purple crystals.
- Cleavage
- Perfect cubic cleavage — it breaks into little cubes, exactly like table salt under a lens.
- Fracture
- Conchoidal, rarely seen
- Specific gravity
- 2.16–2.17 (water = 1)
- Magnetism
- Not magnetic
- Acid test
- No reaction
- UV
- Not fluorescent
Tests that confirm halite
- Tastes salty. This is the classic diagnostic test and it is unambiguous — touch a clean sample with a wet fingertip, not your tongue directly.
- Dissolves readily in water, so specimens must be kept dry.
- Cubic cleavage at hardness 2–2.5.
What halite gets confused with
Each of these is settled by one test. Run that test first.
Calcite's cleavage rhombs lean; halite's cubes are square. Calcite also fizzes in acid.
Sylvite
Sylvite tastes bitter rather than cleanly salty and is slightly softer.
Where it is found
Evaporite deposits, salt domes, desert crusts, and salt mines.
Is it worth anything?
Negligible, though blue halite from certain mines is collectible. Store away from humidity.