gypsum

Today
tell me about gypsym
Gypsum is a very soft, common mineral made of calcium sulfate dihydrate (CaSO₄·2H₂O), widely used in construction, art, and agriculture. It forms in evaporating seas and lakes, appears in several beautiful varieties, and has been used since antiquity.

What gypsum is
Gypsum mineral — a sulfate mineral composed of calcium sulfate dihydrate. It ranks 2 on the Mohs hardness scale, meaning it can be scratched with a fingernail.

Crystal system — monoclinic, often forming clear blades (selenite), silky fibers (satin spar), or fine-grained masses (alabaster).

How gypsum forms
Evaporite formation — Gypsum commonly forms when seawater or saline lake water evaporates, leaving behind layers of calcium sulfate. This is why it appears in desert basins, salt flats, and marine lagoons.

It can also form by hydration of anhydrite, expanding the rock volume by 30–50%.

Where gypsum is found
Occurs worldwide; major producers include Spain, Thailand, the U.S., Turkey, and Russia.

In the U.S., significant deposits occur in New York, Michigan, Virginia, Ohio, Iowa, Kansas, Texas, Nevada, and California.

🪨 Varieties of gypsum
Selenite — clear, glasslike crystals.

Satin spar — fibrous, silky, chatoyant.

Alabaster — fine-grained, used for carving since ancient Egypt and Rome.

Uses of gypsum
Drywall & plaster — the main ingredient in plaster, plaster of Paris, and wallboard.

Fertilizer — improves soil structure and provides calcium and sulfur.

Art & sculpture — alabaster carvings across many civilizations.

Chalk — used in blackboard and sidewalk chalk.

Even found on Mars, where it indicates past liquid water.

Etymology & history
The word gypsum comes from Greek gypsos (“plaster”).

Paris’s Montmartre quarries produced so much calcined gypsum that plaster of Paris became the standard term.