Calcite vs. Gypsum — What's the Difference?

Its crystal structure allows for a wide variety of shapes and sizes.

A soft sulfate mineral, crucial for plaster and drywall.

Calcite's double refraction property splits light into two paths.

Used in agriculture to improve soil structure.

A common naturally occurring mineral, calcite forms in various colors due to impurities.

It forms in sedimentary layers, often associated with limestone.

It's a major component of marine sedimentary rocks.

It's a key ingredient in plaster of Paris.

Calcite reacts with acid to fizz or effervesce.

Gypsum can form transparent crystals called selenite.

Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO3). The Mohs scale of mineral hardness, based on scratch hardness comparison, defines value 3 as "calcite".

Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O. It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, blackboard/sidewalk chalk, and drywall. A massive fine-grained white or lightly tinted variety of gypsum, called alabaster, has been used for sculpture by many cultures including Ancient Egypt, Mesopotamia, Ancient Rome, the Byzantine Empire, and the Nottingham alabasters of Medieval England.

A common crystalline form of natural calcium carbonate, CaCO3, that is the basic constituent of limestone, marble, and chalk. Also called calcspar.

A widespread colorless, white, or yellowish mineral, CaSO4·2H2O, used in the manufacture of plaster of Paris, various plaster products, and fertilizers.

(mineral) a very widely distributed crystalline form of calcium carbonate, CaCO₃, found as limestone, chalk and marble

A mineral consisting of hydrated calcium sulphate. When calcinated, it forms plaster of Paris.

Calcium carbonate, or carbonate of lime. It is rhombohedral in its crystallization, and thus distinguished from aragonite. It includes common limestone, chalk, and marble. Called also calc-spar and calcareous spar.

A mineral consisting of the hydrous sulphate of lime (calcium). When calcined, it forms plaster of Paris. Selenite is a transparent, crystalline variety; alabaster, a fine, white, massive variety.

A common mineral consisting of crystallized calcium carbonate; a major constituent of limestone

A common white or colorless mineral (hydrated calcium sulphate) used to make cements and plasters (especially plaster of Paris)

Gypsum can be identified by its softness, as it can be easily scratched with a fingernail, and its solubility in water.

Its rhombohedral cleavage and reaction with dilute hydrochloric acid, producing bubbles, make calcite easily distinguishable.

Gypsum primarily forms in evaporative environments such as salt flats and lakes where water evaporates, leaving behind sulfate minerals.

Double refraction in calcite has applications in polarized light microscopy and optical instruments.

Its solubility and ability to form a smooth paste that hardens make it ideal for plaster and drywall.

Calcite plays a crucial role in carbon cycling and is a major component of limestone, which can act as a carbon reservoir.

Gypsum is used to improve soil structure, aeration, and water penetration, promoting sustainable agriculture.

Yes, calcite can be used in water treatment as a pH stabilizer and to remineralize demineralized or desalinated water.

Its softness makes it ideal for use in plaster and drywall, as it can be easily shaped, carved, and smoothed.

Calcite is primarily used in the construction industry, particularly in the manufacture of cement and lime.

Yes, food-grade gypsum is used as a coagulant in products like tofu.

Calcite contributes to the landscape through the formation of geological features like stalactites, stalagmites, and limestone mountains.

Calcite forms in a variety of environmental conditions, including marine settings, hot springs, and caves.

Calcite has a Mohs hardness of 3, making it slightly harder than gypsum, which has a hardness of 2.

Calcite is vital in the cement and lime industry, while gypsum is essential in construction for plaster and drywall, both contributing significantly to their respective sectors.