Softest mineral

Talc is the softest mineral on Earth. The Mohs scale of hardness uses talc as its starting-point, with a value of 1. Talc is a silicate (like many of the Earth's most common minerals), and in addition to silicon and oxygen, contains magnesium and water arranged into sheets in its crystal structure. The softness of talc and its perfect cleavage in one direction both owe to weak chemical bonds between adjacent sheets, which can be easily disrupted by scratching or shearing. Because of its softness and cleavage, talc makes a great lubricant in situations where it won't be put under too much stress, as in body powders. Talc is also sectile, which means it can be easily cut or carved. Blocks of talc-rich metamorphic rock, known as soapstone or steatite, are much liked by stone carvers. The earliest steatite carvings were probably ancient Egyptian scarab amulets, which were fired to “dewater” the talc and produce a more resistant form of magnesium silicate able to withstand wear and the trial of time.

This the standard scale used to determine the hardness of solids, especially minerals. It is named after the German mineralogist Friedrich Mohs. The scale reads as given below:

Hardness Material:
1. Talc: easily scratched by the fingernail
2. Gypsum: just scratched by the fingernail
3. Calcite: scratches and is scratched by a copper coin
4. Fluorite: not scratched by a copper coin and does not scratch glass
5. Apatite: just scratches glass and is easily scratched by a knife
6. Orthoclase: easily scratches glass and is just scratched by a file
7. Quartz: not scratched by a file
8. Topaz
9. Corundum
10. Diamond