What type of igneous rock contains large mineral crystals? explain why.

Intrusive igneous rock contains large mineral crystals.
Magma that is trapped beneath Earth's surface is insulated by surrounding rocks, and cools and hardens over very long periods.

Referring to 'large mineral crystals', ones that are seen with the naked eye are called Intrusive (Igneous) Rocks. Since intrusive rocks form when magma cools very slowly, magma that is trapped beneath the Earth's surface is insulated by surrounding rocks, so it cools and hardens over very long periods, thus making the mineral crystals visible. 

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