Question

Amphiboles (commonly hornblende) and pyroxenes (commonly augite) are both silicate minerals that form with the silicon-oxygen tetrahedra in chains. One way in which the minerals can be distinguished from each other is by:

a) Pyroxene's black to dark green color
b) Both minerals can have a hardness of 5.5.
c) Pyroxene has fracture while amphibole has cleavage
d) Pyroxenes have cleavage in two directions at right angles while amphiboles have cleavage in two directions at 56° and 124°.

Answer 1

Amphiboles and pyroxenes are distinguished by their cleavage; amphiboles have cleavage at 56° and 124°, while pyroxenes cleave at 90° angles. These characteristics are critical for identifying the minerals in geological samples and understanding the rocks' formation history.

Step-by-step explanation:

One way in which the minerals amphiboles and pyroxenes can be distinguished from each other is by their cleavage. Amphiboles, commonly known as hornblende, have cleavage in two directions at 56° and 124°, while pyroxenes, commonly known as augite, have cleavage in two directions at right angles (90°). This difference in cleavage angles is a key mineralogical feature and helps geologists identify the minerals within igneous and metamorphic rocks.

Furthermore, understanding the cleavage of these minerals may provide insights into a rock's geologic history and the conditions under which it formed. For instance, amphiboles are often found within igneous rocks like granite or diorite, as well as in some metamorphic rocks, while pyroxenes are common in mafic igneous rocks such as gabbro and basalt.