Alabaster Identification Guide

What Alabaster Looks Like

Alabaster is a fine-grained, massive variety of gypsum (hydrated calcium sulfate, CaSO4·2H2O) used for carving. (Note: ancient/'oriental' alabaster is sometimes banded calcite, but true mineralogical alabaster is gypsum.)

• Color: white, cream, or pale gray, often with subtle translucent cloudiness; can be tinted yellow, pink, or brown by impurities.
• Luster: dull, sugary, to slightly pearly; takes a smooth waxy polish.
• Transparency: translucent — thin pieces let light through softly, a quality prized for lamps and carvings.
• Habit: massive, compact, fine-grained aggregate with no visible crystals; smooth and uniform.

Step-by-Step Field ID Checklist

1. Scratch with a fingernail. True gypsum alabaster is so soft (Mohs ~2) that your fingernail leaves a mark — this is the single best test.
2. Check translucency. Hold a thin edge to light; alabaster glows softly.
3. Feel the weight. It is light for its size (low density).
4. Test with acid. Gypsum alabaster does NOT fizz in dilute acid; if it fizzes vigorously, it is calcite ('onyx-marble' alabaster).
5. Look at the surface. Fine, even, sugary texture with no banding (banding suggests calcite alabaster).
6. Streak. White.

Key Diagnostic Tests

• Hardness: ~2 — scratched by a fingernail. This separates it from nearly all carving stones.
• Acid: no reaction (gypsum); calcite alabaster fizzes.
• Specific gravity: ~2.3 (low).
• Cleavage: gypsum has one perfect cleavage, but in massive alabaster it shows as a sub-conchoidal/splintery fracture.
• Solubility: slightly soluble in water; gypsum can feel slightly soapy and degrades outdoors.
• Streak: white.

Common Look-Alikes and How to Tell Them Apart

• Calcite alabaster (onyx-marble/travertine 'alabaster'): harder (H 3), fizzes in acid, and is usually banded. Alabaster proper (gypsum) is softer and acid-inert.
• Marble: much harder (H 3, calcite) and fizzes in acid; marble cannot be scratched by a fingernail.
• Soapstone (talc): also soft, but talc is even softer (H 1), greasy to the touch, and does not glow translucently the way alabaster does.
• White howlite/magnesite: harder than gypsum; howlite often has gray veining and does not scratch with a nail as easily.
• Marble-look resins/plastics: warmer to the touch, no mineral cleavage, and often show mold marks.

Where Alabaster Is Found

Gypsum alabaster forms in evaporite deposits where seawater or lake water dried up, leaving thick beds of calcium sulfate. Historic and modern sources include Volterra (Tuscany, Italy), Nottingham (England), Spain (Aragon), and many evaporite basins worldwide including the USA. Look for it in sedimentary sequences with other evaporite minerals such as anhydrite, halite, and bedded gypsum.