01 / Origin story
How does gypsum form?
02 / Read the clues
How can you identify gypsum?
Use several clues together.
One photograph shows one specimen, not every variation.
03 / Commonly confused with
Similar at first glance.
Compare the materials side by side.
Photographs are not shown to the same scale.
Gypsum ↗
Very soft — can be scratched with a fingernail (2 on the Mohs hardness scale, one of the softest common rock-forming minerals)
Rock Salt (halite) ↗
Usually clear, white, or tinted pink/orange from impurities
Rock salt — both are soft evaporites, but gypsum doesn't taste salty and doesn't dissolve in water nearly as readily.
04 / Out in the world
Where it’s found.
Ancient evaporated sea and lake basins worldwide — mined extensively as the primary raw material for drywall and plaster.
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