How to Identify Talc: Hardness, Streak, Luster and Tests

The properties that identify Talc — mohs hardness: 1 (The softest known mineral — the reference mineral for hardness 1 on the Mohs scale); luster: Pearly luster; color: Green to white (per one source); white/brown/gray/green (per another source); cleavage or fracture: The two sources disagree: the University of Arkansas page describes cleavage as poorly developed or absent (mostly massive), while the Minerals Education Coalition describes one direction of perfect cleavage that splits into thin sheets. Both are presented as-is without forcing a single answer. Hardness, streak and cleavage are the reliable ones; color alone rarely settles it.

• Touch test: talc has a distinctly soapy or greasy feel.

Common in magnesium-rich rocks such as marble or altered ultramafic rocks; found in Ashland, Florence, Iron, Jackson, Marathon, Marinette, Oneida, and Wood Counties in Wisconsin.

Photograph a fresh, unweathered surface in daylight, then a second shot of any crystal faces or broken edge. Include a coin for scale. If you did a streak test, photograph the streak next to the specimen. The app suggests the likely mineral or rock; confirm with hardness and the tests above before you label it.