Final answer:
Geology is the study of rocks, including igneous rocks. Orthoclase and plagioclase are two common minerals found in igneous rocks, with different characteristics and cleavage directions.
Step-by-step explanation:
The subject of this question is Geology. Geology is the study of rocks and the Earth's history as recorded in the rocks. It involves the identification, classification, and understanding of different types of rocks, including igneous rocks.
Igneous rocks are formed from the solidification of molten material, and they can have different characteristics based on their composition and mineral content. For example, pink orthoclase and white to gray plagioclase are two common minerals found in igneous rocks. They have a pearly to vitreous luster and are harder than glass.
Orthoclase (K-feldspar) is known for its porcelain luster and can be colored pink, white, or gray. It has two cleavage directions at right angles, which can be detected by a reflection of light when the specimen is rotated. Plagioclase, on the other hand, is usually gray or white in granite and has dark-bluish color in gabbro. It also has two cleavage directions at right angles and commonly displays striations.