Talc

Talc is a hydrated magnesium silicate and the softest mineral on the Mohs scale, defining hardness 1. It is a sheet silicate with a distinctly greasy, soapy feel, and can be scratched effortlessly with a fingernail.

It usually occurs as compact, foliated, or fine-grained masses rather than good crystals; the massive variety is called steatite or soapstone. Colors range from white and pale grey to apple green.

Talc is chemically inert, heat-resistant, and an excellent lubricant and filler, making it one of the most useful industrial minerals.

Talc forms mainly by the metamorphism and hydrothermal alteration of magnesium-rich rocks. Two common pathways are the alteration of ultramafic rocks (such as serpentinite and peridotite) and the metamorphism of siliceous dolomites, where dolomite reacts with silica-rich fluids.

It typically develops at relatively low to moderate temperatures along shear zones and contact aureoles, often associated with serpentine, chlorite, and magnesite.

Major producing regions include China, India, the USA (Montana, Texas, Vermont), France, and Finland, frequently in belts of altered ultramafic and carbonate rock.

Talc is unmistakable by its extreme softness (Mohs 1) and greasy, soapy feel — it can be scratched with a fingernail and leaves a slightly slippery residue. It has a pearly to greasy luster, a white streak, and is translucent in thin flakes.

Massive soapstone is easily carved with a knife.

Look-alikes: Pyrophyllite is nearly identical in feel and softness but is an aluminum silicate, hard to distinguish without testing. Gypsum is soft (2) but not greasy. Chlorite and mica are harder and form more clearly elastic sheets. Soapstone's carveability and feel are the giveaways.

Ground talc is a workhorse industrial filler used in paper, paint, plastics, rubber, and ceramics, and as a lubricant and anti-caking agent. Cosmetic-grade talc is the basis of talcum and baby powder, though products must be controlled for asbestos contamination.

Massive soapstone (steatite) is carved into countertops, sinks, wood-stove surrounds, sculptures, and laboratory bench tops because it is soft to work, heat-resistant, and chemically inert.

Historically, soapstone was used for cooking vessels, molds, and 'French chalk' for marking fabric. It has minimal gem value but is popular for carving.