Comparison · Minerals
Anhydrite vs Calcite
Anhydrite and Calcite are easy to confuse because both are minerals. 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 Calcite
- Both sit near Mohs 3–3.5, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
- Hold a thin edge to the light: Anhydrite is Transparent to translucent, Calcite is transparent.
- They overlap in clear, blue, and pink, but Anhydrite also comes in gray and Calcite also comes in yellow, orange, and green.
- Well-formed crystals give it away: Anhydrite is Orthorhombic, Calcite is trigonal.
Anhydrite vs Calcite properties
| Property | Anhydrite | Calcite |
|---|---|---|
| Type | Minerals | Minerals |
| Mohs hardness | 3–3.5 | 3 |
| Luster | Vitreous, pearly on cleavage surfaces | vitreous |
| Streak | White | White |
| Transparency | Transparent to translucent | transparent |
| Specific gravity | 2.9–3.0 | 2.7 |
| Crystal system | Orthorhombic | trigonal |
| Common colors | Colorless, White, Gray, Blue, Pink | Colorless, White, Yellow, Orange, Blue, Green, Pink |
| Rarity | common | common |
| Typical specimen value | $2–$150+ | $2–$100+ |
Which is more valuable?
Anhydrite is usually the more valuable of the two: a typical collector specimen runs about $20 against $15 for Calcite, 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 Calcite
Calcite is one of the most common minerals on Earth, found in sedimentary, metamorphic, and igneous rocks. It's the primary component of limestone and marble.
Anhydrite vs Calcite FAQ
Is Anhydrite the same as Calcite?
No. Both are minerals, but they are distinct species with different hardness, streak or luster. 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 Calcite?
Both sit near Mohs 3–3.5, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Hold a thin edge to the light: Anhydrite is Transparent to translucent, Calcite is transparent. They overlap in clear, blue, and pink, but Anhydrite also comes in gray and Calcite also comes in yellow, orange, and green.
Which is harder, Anhydrite or Calcite?
They are about equally hard, both near Mohs 3–3.5.
Which is more valuable, Anhydrite or Calcite?
Anhydrite is usually the more valuable of the two: a typical collector specimen runs about $20 against $15 for Calcite, and premium Anhydrite can reach $150 or more.
