The passage suggests that the presence of G10 garnet in a kimberlite pipe indicates that:________.
(A) the pipe in which the garnet is found has a 90% chance of containing diamonds
(B) the levels of calcium and chrome in the pipe are conducive to diamond formation
(C) the pipe passed through a diamond-stability field and thus may contain diamonds
(D) any diamonds the pipe contains would not have come from the diamond-stability field
(E) the pipe's temperature was so high that it oxidized any diamonds the pipe might have contained

Diamonds are almost impossible to detect directly because they are so rare: very rich kimberlite Line pipes, the routes through which diamonds rise, may contain only three carats of diamonds per ton of kimberlite. Kimberlite begins as magma in Earth's mantle (the layer between the crust and the core).

As the magma smashes through layers of rock, it rips out debris, creating a mix of liquid and solid material. Some of the solid material it brings up may come from a so-called diamond-stability field, where conditions of pressure and temperature are conducive to the formation of diamonds.

If diamonds are to survive, though, they must shoot toward Earth's surface quickly. Otherwise, they revert to graphite or burn. Explorers seeking diamonds look for specks of indicator minerals.