Talc is known for being the softest mineral on earth. It is number 1 on the Mohs hardness scale, and can be easily scratched by a fingernail. It is not commonly seen in collections, as it is usually uninteresting and fairly common
This is a hydrous magnesium silicate mineral with a chemical composition of Mg3Si4O10(OH)2. Although the composition of talc usually stays close to this generalized formula, some substitution occurs.