In what basic settings do intrusive and extrusive igneous rocks ...

[lindiwe]

In what basic settings do intrusive and extrusive igneous rocks originate?
 
  What will be an ideal response?

Question 2

How does the rate of cooling influence crystal size? What other factors influence the texture of igneous rocks?
 
  What will be an ideal response?

[shayla]

Answer to Question 1

Intrusive rocks originate from cooled and crystallized magma at some depth within the Earth. Extrusive rocks originate from cooled and crystallized lava at the Earth's surface.

Answer to Question 2

Slow rates of cooling allow greater time for crystals to form, so that tends to favor larger crystal size. Fast rates of cooling do not allow time for mineral crystals to form, so the faster the rate, the smaller the crystal size. The composition of the magma or lava and the amount of dissolved gases present also influence crystallization.