Which common rock forming minerals exhibit cleavage planes at nearly 90°?
A)amphiboles like hornblende
B)feldspars like plagioclase and orthoclase
C)pyroxenes like augite
D)both B and C are correct

Question

Quizplus · Accepted Answer

Both feldspars (plagioclase and orthoclase) and pyroxenes (augite) exhibit cleavage planes at nearly 90°. Amphiboles like hornblende, on the other hand, exhibit cleavage planes at angles ranging from 56° to 124°, typically not at nearly 90°.

Which Common Rock Forming Minerals Exhibit Cleavage Planes at Nearly