the formula for area is A=3.14 x r^2, r is radius, found by 380 divided by 2, giving you A=3.14 x 190^2, giving you 113,000. divide by 500, giving you 226, then divide by 70, giving you 3 and a decimal, round up, and you get 4.
A mineral's hardness is a measure of its relative resistance to scratching, measured by scratching the mineral against another substance of known hardness on the Mohs Hardness Scale.
