What can be said about an igneous rock with larger crystals compared to one with smaller crystals?

Answer 1

It has had more time to crystallise

Intrusive igneous rocks are as you described, magma that sits deep in the crust and slowly crystallises.

The main control on crystal growth is time, if a lava is erupted onto the Earth's surface then it has little time to crystallise and therefore the grains are smaller. This could be something like a basalt (which is an extrusive igneous rock):

But if you leave the magma in the crust and give it time to crystallise, then the grains will be much bigger like that of a granite:

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Answer 2

Xavier Atkins

An igneous rock with larger crystals likely cooled more slowly, allowing larger crystals to form. This suggests it formed deeper in the Earth's crust or cooled over a longer period. In contrast, a rock with smaller crystals cooled more rapidly, suggesting it formed closer to the surface or cooled quickly.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.