Comparison · Minerals vs Sedimentary Rocks
Anhydrite vs Rock Salt
Anhydrite and Rock Salt are easy to confuse. Both sit near Mohs 3–3.5, 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 Anhydrite and Rock Salt
- Both sit near Mohs 3–3.5, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
- Anhydrite feels noticeably heavier for its size (specific gravity 2.9–3.0 versus 2.17 for Rock Salt).
- Hold a thin edge to the light: Anhydrite is Transparent to translucent, Rock Salt is opaque.
- They overlap in clear, gray, and pink, but Anhydrite also comes in blue and Rock Salt also comes in orange.
Anhydrite vs Rock Salt properties
| Property | Anhydrite | Rock Salt |
|---|---|---|
| Type | Minerals | Sedimentary Rocks |
| Mohs hardness | 3–3.5 | 2.5 |
| Luster | Vitreous, pearly on cleavage surfaces | vitreous |
| Streak | White | White |
| Transparency | Transparent to translucent | opaque |
| Specific gravity | 2.9–3.0 | 2.17 |
| Crystal system | Orthorhombic | varies |
| Common colors | Colorless, White, Gray, Blue, Pink | Clear, White, Pink, Orange, Gray |
| Rarity | common | common |
| Typical specimen value | $2–$150+ | $1–$75+ |
Which is more valuable?
Anhydrite is usually the more valuable of the two: a typical collector specimen runs about $20 against $10 for Rock Salt, and premium Anhydrite can reach $150 or more.
About Anhydrite
Anhydrite is calcium sulfate, CaSO4, chemically identical to gypsum but lacking the water molecules bound into gypsum's crystal structure. It forms in evaporite basins where seawater or saline lake water concentrates through evaporation, and it readily absorbs water to convert into gypsum, which is why anhydrite outcrops are less common at the surface than at depth. Its name, from the Greek for "without water," directly references this dehydrated composition.
About Rock Salt
Rock Salt is the sedimentary rock form of halite, commonly appearing as clear, white, pink, orange, or gray crystalline salt.
Anhydrite vs Rock Salt FAQ
Is Anhydrite the same as Rock Salt?
No. Anhydrite is a mineral while Rock Salt is a sedimentary rock. Both sit near Mohs 3–3.5, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
How can you tell Anhydrite from Rock Salt?
Both sit near Mohs 3–3.5, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Anhydrite feels noticeably heavier for its size (specific gravity 2.9–3.0 versus 2.17 for Rock Salt). Hold a thin edge to the light: Anhydrite is Transparent to translucent, Rock Salt is opaque.
Which is harder, Anhydrite or Rock Salt?
Anhydrite is harder: Mohs 3–3.5 against Mohs 2.5 for Rock Salt.
Which is more valuable, Anhydrite or Rock Salt?
Anhydrite is usually the more valuable of the two: a typical collector specimen runs about $20 against $10 for Rock Salt, and premium Anhydrite can reach $150 or more.
