Comparison · Minerals
Anhydrite vs Borax
Anhydrite and Borax are easy to confuse because both are minerals. Anhydrite is harder (Mohs 3–3.5) than Borax (Mohs 2–2.5), so Anhydrite will scratch Borax and not the other way round. A fingernail (Mohs 2.5) scratches it easily. Below is a side-by-side comparison of their properties and the quick tests that separate them.
Key differences between Anhydrite and Borax
- Anhydrite is harder (Mohs 3–3.5) than Borax (Mohs 2–2.5), so Anhydrite will scratch Borax and not the other way round. A fingernail (Mohs 2.5) scratches it easily.
- Anhydrite feels noticeably heavier for its size (specific gravity 2.9–3.0 versus 1.7 for Borax).
- They overlap in clear and gray, but Anhydrite also comes in blue and pink.
- Well-formed crystals give it away: Anhydrite is Orthorhombic, Borax is Monoclinic.
Anhydrite vs Borax properties
| Property | Anhydrite | Borax |
|---|---|---|
| Type | Minerals | Minerals |
| Mohs hardness | 3–3.5 | 2–2.5 |
| Luster | Vitreous, pearly on cleavage surfaces | Vitreous to resinous, earthy when dehydrated |
| Streak | White | White |
| Transparency | Transparent to translucent | Transparent to translucent |
| Specific gravity | 2.9–3.0 | 1.7 |
| Crystal system | Orthorhombic | Monoclinic |
| Common colors | Colorless, White, Gray, Blue, Pink | White, Colorless, Gray |
| Rarity | common | common |
| Typical specimen value | $2–$150+ | $2–$150+ |
Which is more valuable?
Typical specimens of Anhydrite and Borax 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 Borax
Borax is a hydrated sodium borate mineral, Na2B4O7·10H2O, that crystallizes from the evaporation of alkaline lakes in arid basins. It has been mined and used by humans for thousands of years as a cleaning agent, flux, and preservative, making it one of the more historically significant evaporite minerals. Borax dissolves readily in water and gives off a sweetish alkaline taste, reflecting its high solubility compared to most rock-forming minerals.
Anhydrite vs Borax FAQ
Is Anhydrite the same as Borax?
No. Both are minerals, but they are distinct species with different hardness, streak or luster. Anhydrite is harder (Mohs 3–3.5) than Borax (Mohs 2–2.5), so Anhydrite will scratch Borax and not the other way round. A fingernail (Mohs 2.5) scratches it easily.
How can you tell Anhydrite from Borax?
Anhydrite is harder (Mohs 3–3.5) than Borax (Mohs 2–2.5), so Anhydrite will scratch Borax and not the other way round. A fingernail (Mohs 2.5) scratches it easily. Anhydrite feels noticeably heavier for its size (specific gravity 2.9–3.0 versus 1.7 for Borax). They overlap in clear and gray, but Anhydrite also comes in blue and pink.
Which is harder, Anhydrite or Borax?
Anhydrite is harder: Mohs 3–3.5 against Mohs 2–2.5 for Borax.
Which is more valuable, Anhydrite or Borax?
Typical specimens of Anhydrite and Borax trade in a similar range, around $20.
