What mineral has the least hardness according to the scale?

The softest mineral in the Mohs Hardness Scale is talc.

Talc is often used in baby powder and corn starch, among other things. Talc cleaves into thin sheets, and it is held together only by van de Waals bonds, which allows these sheets to slip past each other. This gives the mineral its softness and it is often valued as a high-temperature lubricant.