Question

41. Apply what you've learned: Based on grain size, which rock type is most likely to be a volcanic rock? a gabbro b. diorite c. granite d andesite

Answer 1

Answer:

d. andesite

Explanation:

Volcanic rocks, also known as extrusive rocks, forms when the magma (called lava once it reaches the surface), flows onto Earth’s surface. The texture of the rock is determined by the rate of cooling, the slower the rock cools, the larger the crystals form, therefore, volcanic rocks present fine-grained or aphanitic to glassy texture because they cool relatively quickly and under low pressures.

Considering this we'll now analyze each option given:

• Gabbro is an intrusive igneous rock, this means it cools down slowly forming large crystals, therefore it's not volcanic.
• Diorite is an intrusive igneous rock composed principally of the silicate minerals, similar to gabbro it's not volcanic.
• Granite is a coarse- or medium-grained intrusive igneous rock that is rich in quartz and feldspar, therefore is not a volcanic rock
• Andesite is the name used for a family of fine-grained, extrusive igneous rocks that are usually light to dark gray in color. Since it's extrusive this one is the correct answer.

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