What rock type is the hardest and what is the softest?

The softest rock would be Talc.
 

The hardest rock would be Diamond. 

Hardest rock: Diamond. Although diamond is still considered the hardest, the bulk modulus of the metal osmium has recently been found to be 476 GPa.

Softest Rock: Sedimentary rocks form a thin layer of rock over 75 per cent of the Earth's surface. 

Hope this helps :))

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