Comparison · Minerals
Anhydrite vs Aragonite
Anhydrite and Aragonite 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 Aragonite
- Both sit near Mohs 3–3.5, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
- They overlap in clear, gray, blue, and pink, but Aragonite also comes in yellow.
Anhydrite vs Aragonite properties
| Property | Anhydrite | Aragonite |
|---|---|---|
| Type | Minerals | Minerals |
| Mohs hardness | 3–3.5 | 3.5–4 |
| Luster | Vitreous, pearly on cleavage surfaces | Vitreous to resinous |
| Streak | White | White |
| Transparency | Transparent to translucent | Transparent to translucent |
| Specific gravity | 2.9–3.0 | 2.93–2.95 |
| Crystal system | Orthorhombic | Orthorhombic |
| Common colors | Colorless, White, Gray, Blue, Pink | Colorless, White, Yellow, Gray, Blue, Pink |
| Rarity | common | common |
| Typical specimen value | $2–$150+ | $2–$150+ |
Which is more valuable?
Typical specimens of Anhydrite and Aragonite trade in a similar range, around $20.
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 Aragonite
Aragonite is calcium carbonate, CaCO3, crystallizing in the orthorhombic system as a metastable polymorph of the more common mineral calcite. It readily forms in low-temperature settings such as caves, hot springs, and the shells of many marine organisms, and it slowly converts to calcite over geologic time. Twinned crystal clusters resembling six-rayed stars are among its most recognizable forms.
Anhydrite vs Aragonite FAQ
Is Anhydrite the same as Aragonite?
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 Aragonite?
Both sit near Mohs 3–3.5, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. They overlap in clear, gray, blue, and pink, but Aragonite also comes in yellow.
Which is harder, Anhydrite or Aragonite?
Aragonite is harder: Mohs 3.5–4 against Mohs 3–3.5 for Anhydrite.
Which is more valuable, Anhydrite or Aragonite?
Typical specimens of Anhydrite and Aragonite trade in a similar range, around $20.
