Identification guide · Minerals
How to Identify Anhydrite
Anhydrite is usually white, gray, or bluish-gray, occasionally with violet or pink tints, and has a vitreous to pearly luster on cleavage surfaces. Its hardness of 3 to 3.5 is close to gypsum's, but anhydrite is harder and denser, and it shows three cleavage directions at right angles compared to gypsum's single perfect cleavage. The streak is white, and massive anhydrite can resemble marble or fine-grained gypsum, so a hardness test and cleavage check are needed to tell them apart reliably.
Anhydrite identification checklist
| Color | Colorless, White, Gray, Blue, Pink | Look at a clean, dry surface in daylight. Color zoning, banding or spots are as diagnostic as the hue. |
|---|---|---|
| Luster | Vitreous, pearly on cleavage surfaces | Fresh surfaces shine like glass; a dull surface usually means weathering, so chip or wet a corner. |
| Transparency | Transparent to translucent | Hold a thin edge up to a bright light and note whether light passes through. |
| Mohs hardness | 3–3.5 | A copper coin (Mohs 3.5) scratches it, but a fingernail does not. |
| Streak | White | Drag a corner across unglazed porcelain (the back of a bathroom tile) and check the powder color. |
| Cleavage | Perfect in three directions at right angles | |
| Fracture | Uneven to splintery | |
| Specific gravity | 2.9–3.0 | Ordinary rock-like heft (specific gravity about 2.95), similar to quartz. |
| Crystal system | Orthorhombic |
Anhydrite look-alikes and how to tell them apart
Anhydrite is harder (Mohs 3–3.5) than Gypsum (Mohs 2), so Anhydrite will scratch Gypsum and not the other way round. A fingernail (Mohs 2.5) scratches it easily. Anhydrite vs Gypsum →
Anhydrite is harder (Mohs 3–3.5) than Selenite (Mohs 2), so Anhydrite will scratch Selenite and not the other way round. A fingernail (Mohs 2.5) scratches it easily. Anhydrite vs Selenite →
Both sit near Mohs 3–3.5, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Anhydrite vs Calcite →
Anhydrite is harder (Mohs 3–3.5) than Alabaster (Mohs 1.5–2), so Anhydrite will scratch Alabaster and not the other way round. A fingernail (Mohs 2.5) scratches it easily. Anhydrite vs Alabaster →
Anhydrite identification FAQ
How can you tell if a rock is Anhydrite?
Check the color (colorless, white, gray, and blue), the vitreous, pearly on cleavage surfaces luster, a Mohs hardness of 3–3.5 and a white streak. Photographing it with the StoneSnap app gives a match in seconds.
What is the hardness of Anhydrite?
Anhydrite has a Mohs hardness of 3–3.5. A copper coin (Mohs 3.5) scratches it, but a fingernail does not.
What is the difference between Anhydrite and Gypsum?
Anhydrite (Mohs 3–3.5, vitreous, pearly on cleavage surfaces luster) and Gypsum (Mohs 2, vitreous, pearly, or silky (fibrous), earthy when massive luster) look alike, but hardness, streak and heft usually separate them. See the full Anhydrite vs Gypsum comparison for a side-by-side table.
Is Anhydrite worth anything?
Entry-level Anhydrite specimens sell for around $2, typical collector pieces about $20, and premium examples $150 or more depending on size, quality and locality.
What color is Anhydrite?
Anhydrite is most often colorless, white, gray, and blue. Color varies with impurities and locality, so confirm with hardness and luster rather than color alone.
