Industrial Minerals · Buyer's Guide
Anhydrite: Export Buyer's Guide to Natural Calcium Sulfate
Anhydrite is natural calcium sulfate without crystal water (CaSO4). It is traded under HS 2520.10 together with natural gypsum, and its main buyers are cement plants, calcium-sulfate screed producers and agriculture. This guide covers how it differs from gypsum, where it is used, what to specify in a request for quotation, and how to ship it.
Anhydrite vs gypsum at a glance
Both minerals are calcium sulfate. The difference is water: gypsum carries about 21% crystal water by weight, anhydrite carries none. That single difference drives most of the commercial trade-offs below.
| Property | Anhydrite | Gypsum |
|---|---|---|
| Formula | CaSO4 | CaSO4·2H2O |
| Crystal water | 0% | 20.9% |
| SO3 content (pure mineral) | 58.8% | 46.5% |
| Mohs hardness | 3.5 | 1.5–2 |
| Specific gravity | 2.97 | 2.31–2.33 |
| In contact with water | Slowly converts to gypsum | Stable |
SO3 and water figures are calculated from molar masses. Because anhydrite carries about 26% more SO3 per tonne, a buyer needs roughly 21% less of it than gypsum to add the same amount of sulfate.
Where anhydrite is used
Cement set retarder
A published study found natural anhydrite to be a very efficient setting retarder with no significant change in cement properties, at an optimum sulfate addition of around 3.5%. It suits low-aluminate and slag cements best; its slower dissolution can upset setting in cements high in alkali or aluminate.
In vertical roller mills, blending it with gypsum (50:50 or 25:75 gypsum to anhydrite) reduces the crystal water that causes build-up and coating in silos.
Calcium sulfate floor screeds
Anhydrite is the binder in self-levelling calcium sulfate screeds, classed CA under EN 13813. They shrink less than cement screeds and conduct heat well, which makes them common over underfloor heating. They are for dry interiors only.
Soil amendment
Crushed anhydrite supplies calcium and sulfur to soil like gypsum does. With no crystal water, each tonne delivers more calcium than a tonne of gypsum.
Plaster and industrial uses
It is an ingredient in plaster and other construction products, and small amounts serve as a drying agent in plaster, paint and varnish.
What to specify in your request for quotation
Suppliers price anhydrite on chemistry and sizing. State these so quotes are comparable:
- CaSO4 or SO3 content, as a minimum percentage on a dry basis
- Combined water, to confirm how much of the material is anhydrite rather than gypsum
- Free moisture, which affects both weight paid for and handling
- Grain size, for example 0–50 mm or 10–60 mm crushed rock, or a ground powder for screeds
- Impurity limits your process cares about, such as chloride, MgO and insoluble residue
- Quantity, packaging, Incoterm and destination port
- Inspection: a certificate of analysis per lot, and third-party inspection if the contract needs it
Customs classification and shipping
- HS 2520.10 covers natural gypsum and anhydrite. Calcined plasters fall under HS 2520.20, so do not mix the two on your documents. Check the national tariff line at your destination with the HS Code Explorer.
- Keep it dry. Anhydrite converts to gypsum when exposed to water, so cover stockpiles and specify clean, dry holds or containers.
- Bulk or containers. Large tonnages usually move in bulk carriers; smaller lots move in 20ft containers, where dense minerals reach the weight limit before the volume limit. Check limits in the container specifications library and plan the load with the CBM calculator.
- Price the full cost. Compare FOB and CFR offers with the Incoterms® 2020 guide and the landed cost calculator.
About this guide
This is independent reference information for buyers and specifiers. IMPUTIX is published by Mada Trade Co. in Alexandria; the guide is not an offer to sell this material, and product availability should always be confirmed with your own suppliers.
Shipping a bulk mineral? See export packaging for FIBC bulk bags and export packaging options.
Market context: industrial minerals market research. Other mineral guides: Metakaolin · Calcined shale · Perlite.
Frequently asked questions
What is the difference between anhydrite and gypsum?
Both are calcium sulfate. Gypsum (CaSO4·2H2O) holds about 21% crystal water; anhydrite (CaSO4) holds none, so it is harder, denser and richer in SO3.
What is the HS code for anhydrite?
Natural anhydrite is classified under HS 2520.10, “Gypsum; anhydrite”. Calcined plasters are HS 2520.20. National tariff lines add further digits.
Can anhydrite replace gypsum in cement?
Yes, partly or fully, according to published cement research, particularly in low-aluminate and slag cements. Plants usually test blends first, because anhydrite dissolves more slowly and shortens setting time as its share rises.
How should anhydrite be stored?
Dry and covered. In contact with water it gradually converts to gypsum, which changes its chemistry and handling.
Sources
- Anhydrite — Wikipedia (formula, hardness, specific gravity)
- Gypsum — Wikipedia (hardness, specific gravity)
- Anhydrite: uses and properties — Geology.com
- Alternative calcium sulfate-bearing materials as cement retarders, Part I: Anhydrite — Cement and Concrete Research
- Effects of alternative calcium sulphate-bearing materials in vertical mills — Case Studies in Construction Materials
- Anhydrite screed: what it is and how it works (EN 13813 CA class)
Last reviewed: September 2026.