Anhydrite is an orthorhombic calcium-sulfate mineral with the formula CaSO₄. It commonly occurs as white or gray cleavage masses, evaporite beds and thick tabular crystals, while transparent specimens may be colorless, pale blue, violet, pink or brown.
Anhydrite at a Glance
| Property | Anhydrite |
|---|---|
| Mineral group | Sulfate |
| Composition | Calcium sulfate, CaSO₄ |
| Colors | Colorless, white, gray, pale blue, violet, pink, red-brown and brown |
| Crystal system | Orthorhombic |
| Habit | Thick tabular, equant, prismatic, granular, fibrous, nodular and massive |
| Luster | Vitreous, pearly or greasy |
| Transparency | Transparent to translucent; massive material may be opaque |
| Mohs hardness | About 3–3.5 |
| Cleavage | Perfect to near-perfect in three directions |
| Tenacity | Brittle |
| Common use | Mineral specimens, cement and screed products, soil treatment and industrial fillers |
| Main care concern | Cleavage, scratching, hydration, moisture-sensitive matrix and impact |
Mindat’s anhydrite data document its orthorhombic structure and its equant, tabular, fibrous, granular and massive habits.
What Is Anhydrite?
Anhydrite is the water-free calcium-sulfate mineral. Its name comes from a Greek term meaning “without water,” distinguishing it from gypsum, which contains two water molecules in its crystal structure.
The minerals are chemically related:
- Anhydrite: CaSO₄.
- Gypsum: CaSO₄·2H₂O.
- Bassanite: approximately CaSO₄·0.5H₂O.
Anhydrite is not simply dried gypsum in every geological occurrence. It can crystallize directly under suitable temperature, pressure and salinity conditions or form when gypsum loses structural water.
How Anhydrite Forms
The largest anhydrite deposits occur in evaporite basins where seawater or saline lake water becomes concentrated. It is commonly interbedded with halite, gypsum, dolomite and limestone in sedimentary sequences that may reach substantial thickness.
Anhydrite also forms in hydrothermal veins, salt-dome cap rock, geothermal systems and altered carbonate rocks. In hot saline fluids, CaSO₄ may precipitate as anhydrite rather than gypsum.
Modern research shows that calcium-sulfate crystallization can involve the aggregation and reorganization of nanoscale precursor particles. Studies of large Naica anhydrite crystals have identified internal structural imperfections recording this non-classical growth process.
Anhydrite Meaning and Symbolism
Traditional mineral symbolism associates anhydrite with structure, restraint and working within practical limits. Its relationship with gypsum also inspires metaphors involving dehydration, renewal and changes in environmental conditions.
These are traditional metaphysical interpretations rather than scientifically demonstrated emotional, medical or psychological effects.
An anhydrite specimen may be used as a personal reminder to create clearer boundaries or simplify an overcomplicated process without presenting the mineral as a treatment.
Anhydrite Colors
Pure transparent anhydrite is colorless. White and gray are common in massive evaporite material because of grain boundaries, inclusions and associated minerals.
Pale blue and violet transparent crystals are particularly attractive to collectors. Pink, reddish and brown colors may result from iron compounds, lattice defects or finely dispersed inclusions.
The light blue-gray Peruvian lapidary material sold as Angelite is a trade variety of massive anhydrite rather than a separate mineral species.
Anhydrite vs. Gypsum
The defining difference is structural water. Anhydrite contains no water in its ideal formula, while gypsum contains two water molecules per formula unit.
Gypsum is softer, with a Mohs hardness near 2, and can generally be scratched with a fingernail. Anhydrite is harder at approximately 3–3.5 and has a denser, more compact feel.
Water can convert anhydrite toward gypsum under suitable conditions, although the speed depends on grain size, defects, temperature, chemistry and physical activation. Research on industrial binders shows that grinding and chemical activators can substantially accelerate hydration.
The hydrated mineral is covered in the Gypsum guide.
Anhydrite vs. Celestite and Barite
Anhydrite, celestite and barite are all sulfate minerals, but they contain different principal cations.
Anhydrite contains calcium, celestite contains strontium and barite contains barium. Celestite and barite are noticeably denser than anhydrite, especially when pieces of similar dimensions are compared.
Crystal habit can overlap, so density, refractive properties and chemical analysis may be needed for reliable identification.
Important Anhydrite Localities
The historic discovery locality is associated with the Hall in Tirol salt deposits in Austria. Evaporite anhydrite is widespread across Europe, North America, the Middle East and other former marine basins.
The Naica district in Chihuahua, Mexico, produced unusually large transparent to translucent crystals in hydrothermal cavities. Academic studies of these crystals have investigated both their growth structure and mesocrystalline defects.
Other collector localities include Stassfurt in Germany, the Simplon region of Switzerland, Poland, Canada and several mining districts in Peru. Massive industrial material occurs far more widely than attractive display crystals.
Is Anhydrite a Gemstone?
Transparent anhydrite can be faceted, but it is a specialist collector gem rather than a mainstream jewelry stone.
Its limitations are significant:
- Three strong cleavage directions complicate cutting and setting.
- Hardness near 3.5 allows rapid scratching.
- Transparent clean crystals are uncommon.
- Many fine crystals are more valuable intact as specimens.
Faceted stones are usually small ovals, cushions or step cuts. The cutter must orient the rough around cleavage and avoid thin corners that can break during polishing.
Cabochons are more common in massive blue Angelite than in transparent crystalline anhydrite. For jewelry, earrings and protected pendants are more realistic than rings or bracelets.
Industrial Uses of Anhydrite
Most anhydrite is not sold as a collectible gemstone. Industrial grades are ground and used in construction materials, cement chemistry, self-leveling screeds, fillers and some soil-conditioning products.
Commercial mineral suppliers market anhydrite for its low crystal-water content, whiteness and controlled behavior in binder systems.
These industrial products should not be confused with display specimens. Construction-grade anhydrite is valued for chemical and particle-size specifications rather than color, transparency or crystal form.
How Anhydrite Is Sold
Collector material is usually sold as:
- Small cleavage crystals or thumbnails.
- Miniatures with transparent crystals on matrix.
- Cabinet specimens from evaporite or hydrothermal localities.
- Massive colored material for cabochons and carvings.
- Rare loose faceted stones.
Anhydrite rough intended for cutting should be sold with clear disclosure of fractures, cleavage orientation and locality. Ordinary massive white industrial material has little gem value.
Anhydrite Price and Value
Indicative July 2026 retail asking-price ranges are:
| Anhydrite form | Approximate retail range |
|---|---|
| Common massive specimen | $5–$25 |
| Small crystal thumbnail | $15–$60 |
| Attractive transparent or colored miniature | $60–$250 |
| Fine locality or large crystal specimen | $250–$1,000+ |
| Commercial cabochon | About $5–$40 |
| Rare faceted transparent anhydrite | About $20–$150+ per carat |
Wholesale references place inexpensive anhydrite cabochons near $0.10 per carat and many carvings between approximately $5 and $40, while specialist blue cabochons can cost more.
Fine Naica crystals, documented historic specimens and unusually transparent violet material are specimen-market items and may exceed the general range. No standardized price guide exists because condition, locality and crystal form matter more than weight alone.
How to Identify Anhydrite
Three strong cleavage directions are an important clue. Broken massive material often shows blocky surfaces with pearly or glassy reflections.
Other useful observations include:
- Hardness greater than gypsum but lower than fluorite.
- White streak.
- Specific gravity close to 3.
- Orthorhombic tabular or blocky crystals.
- Association with halite, gypsum, calcite or sulfide minerals.
Anhydrite may be confused with gypsum, calcite, celestite, barite or pale feldspar. Destructive acid and scratch tests should be avoided on valuable specimens.
Begin with the non-destructive workflow in How to Identify Crystals.
Anhydrite Hardness and Durability
Anhydrite’s hardness of 3–3.5 offers little resistance to jewelry abrasion. Copper, steel tools, quartz-rich dust and common gemstones can scratch it.
The three cleavage directions create an additional risk. A sharp blow can split a crystal along a smooth plane even if the surface has few scratches.
Its position relative to common gems appears in the Gemstone Hardness Chart.
Can Anhydrite Go in Water?
Routine soaking is not recommended. Anhydrite can hydrate toward gypsum under suitable conditions, and water can enter cleavage cracks, affect matrix minerals or mobilize surface residue.
A brief rinse will not necessarily transform a dense specimen immediately. The risk increases with fine-grained material, damaged surfaces, prolonged contact, warm water and repeated wet-dry cycles.
Do not use anhydrite in direct-contact drinking-water preparations. Review the broader rules in Which Crystals Can and Cannot Go in Water.
How to Clean Anhydrite
Dust stable crystals with a soft dry brush. Use a barely damp cloth on durable massive material only when necessary, then dry it immediately.
Avoid ultrasonic cleaners, steam, acids, abrasive powders and prolonged rinsing. Vibration can exploit cleavage, while water may affect alteration surfaces or associated evaporite minerals.
Large crystals should be supported from the matrix. Never lift a specimen by a projecting anhydrite crystal.
How to Store Anhydrite
Store each specimen in a rigid box with padding beneath the matrix. Keep crystal faces away from direct pressure and do not allow loose specimens to strike one another.
Maintain a dry, stable environment. Damp basements, bathrooms and repeated humidity changes are poor storage conditions for calcium-sulfate specimens.
Preserve original locality labels because documented mine or formation information can materially affect scientific and collector value.
Frequently Asked Questions
Is anhydrite the same as gypsum?
No. Anhydrite is CaSO₄, while gypsum is CaSO₄·2H₂O and contains structural water.
Is Angelite anhydrite?
Yes. Angelite is the trade name used for pale blue-gray massive anhydrite from Peru.
Can anhydrite turn into gypsum?
Yes, under suitable conditions anhydrite can absorb water and hydrate toward gypsum.
Is anhydrite rare?
The mineral is widespread in evaporite deposits, but transparent display crystals and faceting-grade material are uncommon.
Can anhydrite be used in rings?
It is not a practical daily-wear ring stone because it is soft, brittle and strongly cleavable.
What is anhydrite used for?
Industrial material is used in cement, screed binders, fillers and soil-related products. Collector material is sold as crystals, locality specimens and occasional gems.
Browse additional mineral-species profiles in the Gemstone Guides collection.
Disclaimer: Anhydrite’s symbolic meanings are traditional beliefs, not scientifically proven effects or medical advice. Do not ingest mineral material or place anhydrite directly in drinking water.
