Question

extrusive igneous rocks generally have small crystals why

Answer 1

Intrusive rocks have large crystals that can be seen with the naked eye. Extrusive igneous rocks come from lava. Lava, at the surface, is exposed to air and water which causes the molten rock to cool rapidly. Solidifying rocks at the surface cool too quickly for large crystals to form.

Answer 2

Answer:

Extrusive or volcanic rocks:

These rocks are formed when magma breaks through the crust and reaches the surface of the earth (where it is called lava). It cools rapidly and solidifies to form rocks. The common rocks formed in this manner are basalt and obsidian.

Instrusive or plutonic rocks:

These rocks are formed when magma fails to break through the crust and cools slowly under the crust  forming rocks. Because of slow cooling it solidifies into rocks with large grains of crystals. The common eg of rocks formed in this manner are granite and dolerite.

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Explanation: