Which of the following rocks cooled at the lowest temperature: rhyolite, andesit

Question

Which of the following rocks cooled at the lowest temperature: rhyolite, andesite, or basalt? How do you know?

Why are igneous rocks classified on the basis of texture and composition instead of size and shape of the rock?

Which of the following rocks cooled quickly from a volcano: obsidian or diorite?

If you found quartz in an igneous rock, what other minerals would you expect to find?

If you found olivine in an igneous rock, what other minerals would you expect to find?

Would you expect to find olivine and quartz in the same rock? Explain your answer

Explanation / Answer

A) Rhyolite, as it is primarily composed of silica SiO2. It is higly viscous and has temperature < 1173 Kelvin

B) Texture basically defines how it is formed and refers to the presence and absence of certain individual mineral crystals, their sizes and orientation and development. It also predicts the cooling rate during formation and therefore it gives certain information as to the depth of formation. Composition defines the percent composition of minerals in a rock. Based on composition, igneous rock belongs in either one of five categories: rhyolitic, andesitic, basaltic , peridotitic and ultramafic.

Size, color and shape doesnot truly defines a rock and cannot be used to predict the formation period, cooling rate mineral compostion.

C) Obsidian cools quickly

D) Feldspar, Mica

E) Amphibole, Feldspar, Pyroxene

F) Yes, we can find both together in Peridotite

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