Q 17

Which statement best describes the crystallization of magmas? A)Early formed crystals are big and irregular in shape, but gradually get smaller and have better developed faces with time as they react with the residual melt. B)A felsic magma produces only one rock type equal to the melt composition by crystallizing quartz, feldspar, and ferromagnesian minerals in fixed proportions and compositions until all of the melt is used up. C)During crystallization, which can occur over an interval of about 200° C, the composition of the residual melt continuously changes as particular ions are selectively removed and incorporated into certain minerals that crystallize early at high temperature. D)Like the freezing of water, cooling magmas hit their crystallization temperature and stop cooling until all the melt has crystallized, whereupon cooling resumes.

Multiple Choice