Question

question 20 of 20 :
select the best answer for the question.

1. a geologist discovers a sample of fine - grained rock made up of very small crystals. based on its physical appearance, what can the geologist conclude about the rock?

a. it formed from materials produced by living organisms.
b. it formed from the remains of living organisms.
c. it formed from magma that cooled slowly.
d. it formed from magma that cooled quickly.
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Explanation:

To solve this, we analyze each option:

• Option A: Rocks from living - organism - produced materials (like some biochemical processes) don't relate to crystal size from cooling. Eliminate A.
• Option B: Rocks from remains of living organisms (fossil - fuel - related or organic - sedimentary) also don't relate to crystal size from cooling. Eliminate B.
• Option C: Magma cooling slowly (like intrusive igneous rocks) forms large crystals. But the rock has small crystals, so C is wrong.
• Option D: Magma cooling quickly (like extrusive igneous rocks, e.g., basalt) forms fine - grained rocks with small crystals. This matches the description.

Answer:

D. It formed from magma that cooled quickly.