An igneous rock is found on the ground and has no identifiable crystals. What is the most likely origin of this rock?

Question

molten material that cooled slowly
molten material that cooled quickly
rock that was eroded by surrounding rocks
rock that was exposed to extreme pressure

Answer 1

The igneous rock you found, which has no identifiable crystals, most likely originated from molten material that cooled quickly. When magma cools rapidly, as it does when it erupts onto the surface as lava, it does not have enough time to form large crystals, resulting in a glassy or acryphal texture, often seen in rocks like obsidian or basalt. In contrast, rocks that cool slowly typically have larger, identifiable crystals.