Question

Question #7221f

Answer 1

Graphite is the most stable allotrope at room temperature and normal pressure. However, diamond can become stable at high enough pressure.

Explanation:

A carbon phase diagtam may be found here:

http://dao.mit.edu/8.231/CarbonPhaseDia.htm

Diamond is more stable at high pressure because it is denser, and high pressure tends to favor denser phases.

Diamond is commonly made synthetically by putting graphite under high pressure, and also high temperature plus a catalyst to make the transformation go at a feasible rate.