(Q020) Diamonds a. are brought from the mantle to the surface in magma that hardens into kimberlite. b. are found in carrot-shaped structures called pegmatites. c. of industrial quality (non-gem quality) have no use and are usually discarded. d. are exceedingly rare, which is why their price is so high.

A. are brought from the mantle to the surface in magma that hardens into kimberlite

Explanation:

Diamonds are brought to the surface from the mantle in a magma that is known as the kimberlite. This kimberlites is rich in gases and it is an igneous rock that has the following minerals,olivine, phlogophite, serpentine etc.

The origination of diamonds in the mantle happens as carbon transformation occurs due to heat and pressure occurs. The kimberlite pipes and what brings the diamonds to the surface