Final answer:
Granite and obsidian have different cooling rates due to their composition and formation processes. Granite forms slowly, allowing for the growth of visible crystals, while obsidian forms rapidly, resulting in a glassy texture without any crystals.
Step-by-step explanation:
Granite and obsidian have different cooling rates due to their composition and formation processes. Granite is an igneous rock that forms from the slow cooling and solidification of molten magma deep within the Earth's crust. This slow cooling allows for the formation of visible crystals, giving granite its coarse-grained texture. On the other hand, obsidian forms from very rapid cooling of lava or high-viscosity lava, which prevents the formation of crystals. As a result, obsidian has a smooth, glassy texture without any visible crystals.
The differences in cooling rates can be observed in the appearance and texture of the two rocks. Granite has a coarse-grained texture with visible minerals, while obsidian has a smooth, glassy texture without any visible minerals or crystals. Additionally, the sharpness of freshly-broken obsidian and the lack of sharp edges in granite can also be attributed to their different cooling rates.
In summary, the difference in cooling rate between granite and obsidian can be explained by the speed at which the rocks solidify and the formation of crystals. Granite forms slowly, allowing for the growth of visible crystals, while obsidian forms rapidly, resulting in a glassy texture without any crystals.
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