Comparison · Minerals vs Sedimentary Rocks
Gypsum vs Rock Salt
Gypsum and Rock Salt are easy to confuse. Both sit near Mohs 2, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Below is a side-by-side comparison of their properties and the quick tests that separate them.
Key differences between Gypsum and Rock Salt
- Both sit near Mohs 2, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
- Hold a thin edge to the light: Gypsum is Transparent to translucent, Rock Salt is opaque.
- They overlap in clear, gray, and pink, but Gypsum also comes in yellow and brown and Rock Salt also comes in orange.
Gypsum vs Rock Salt properties
| Property | Gypsum | Rock Salt |
|---|---|---|
| Type | Minerals | Sedimentary Rocks |
| Mohs hardness | 2 | 2.5 |
| Luster | Vitreous, pearly, or silky (fibrous), earthy when massive | vitreous |
| Streak | White | White |
| Transparency | Transparent to translucent | opaque |
| Specific gravity | 2.3–2.35 | 2.17 |
| Crystal system | Monoclinic | varies |
| Common colors | Colorless, White, Gray, Yellow, Brown, Pink | Clear, White, Pink, Orange, Gray |
| Rarity | common | common |
| Typical specimen value | $2–$150+ | $1–$75+ |
Which is more valuable?
Gypsum is usually the more valuable of the two: a typical collector specimen runs about $20 against $10 for Rock Salt, and premium Gypsum can reach $150 or more.
About Gypsum
Gypsum is a soft, common evaporite mineral, calcium sulfate dihydrate with the formula CaSO4·2H2O, that defines hardness 2 on the Mohs scale and can be scratched with a fingernail. It precipitates from evaporating saline water and occurs in forms ranging from transparent selenite crystals to fibrous satin spar and massive alabaster. Gypsum is also the principal raw material used to manufacture plaster of Paris and drywall.
About Rock Salt
Rock Salt is the sedimentary rock form of halite, commonly appearing as clear, white, pink, orange, or gray crystalline salt.
Gypsum vs Rock Salt FAQ
Is Gypsum the same as Rock Salt?
No. Gypsum is a mineral while Rock Salt is a sedimentary rock. Both sit near Mohs 2, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
How can you tell Gypsum from Rock Salt?
Both sit near Mohs 2, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Hold a thin edge to the light: Gypsum is Transparent to translucent, Rock Salt is opaque. They overlap in clear, gray, and pink, but Gypsum also comes in yellow and brown and Rock Salt also comes in orange.
Which is harder, Gypsum or Rock Salt?
Rock Salt is harder: Mohs 2.5 against Mohs 2 for Gypsum.
Which is more valuable, Gypsum or Rock Salt?
Gypsum is usually the more valuable of the two: a typical collector specimen runs about $20 against $10 for Rock Salt, and premium Gypsum can reach $150 or more.
