Diamonds are very hard gemstones that form Choose one:

a. from biomineralization like an oyster pearl.
b. when graphite is subjected to high pressure.
c. by precipitation in a freshwater lake.
d. when quartz and other silicate minerals are subjected to high pressure.

B. when graphite is subjected to high pressure.

Explanation: Diamond is a gem stone formed as a result of high pressure heating of graphite. Diamond are one the most sort after Gem stones in the world, used right from ancient times as a decorative substance and material.

Diamonds are fluorescent in nature and has been used for making diamond rings and other ornaments, Diamonds are known to be colourless and that describes its highest quality.

when graphite is subjected to high pressure.

Explanation: Diamond is a glimmering glass-like mineral that is an allotrope of carbon in which each atom is surrounded by four others in the form of a tetrahedron.

Most natural diamonds have ages between 1 billion and 3.5 billion years. Most were formed at depths between 150 and 250 kilometres.

Synthetic diamonds can be grown from high-purity carbon under high pressures and temperatures.

Graphite subjected to high pressure and temperature can be said to be an example of synthetic formation of diamond.

i'm sure the answer you are looking for would be

a. an ice age

hope this contact me if this didn't or you need with more answers : )