easy · Act science
In oceanic basalt formations, the presence of certain olivine crystals can indicate the rate of cooling. Rapidly cooled 'quenched' basalt typically exhibits a microcrystalline structure, whereas basalt that cools slowly deep within the crust develops larger, well-defined crystals. A researcher observes a formation with large crystals at the center but a glass-like microcrystalline texture on the outer edges.
What is the most likely inference regarding the formation of this basaltic body?
- Larger olivine crystals are denser than microcrystalline basalt, meaning they naturally sink to the center of a molten body before the cooling process begins.
- The entire formation cooled at a uniform rate, but the internal chemical composition of the core favored large crystal growth over the microcrystalline edges.
- The outer surface of the basaltic body was in direct contact with a significantly cooler medium, such as seawater, which accelerated the cooling process at the boundary.
- Basaltic formations deep within the crust always contain large crystals because the pressure of the overlying rock prevents the formation of microcrystals.
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