What characteristic should be used to determine if an igneous rock is intrusive or extrusive? *
color
crystal size
shape
age
From Google. "Intrusive igneous rocks cool from magma slowly in the crust. They have large crystals. Extrusive igneous rocks cool from lava rapidly at the surface. They have small crystals."
The characteristic that should be used to determine if an igneous rock is intrusive or extrusive is crystal size.
The characteristic that should be used to determine if an igneous rock is intrusive or extrusive is crystal size.
To understand why crystal size is used, let's start by understanding the difference between intrusive and extrusive rocks. Intrusive rocks are formed underground when molten magma cools and solidifies slowly. This slow cooling allows the minerals in the magma to grow larger crystals. On the other hand, extrusive rocks are formed on the Earth's surface when lava erupts and cools rapidly.
Crystal size can be used as a distinguishing feature because intrusive rocks typically have larger crystals compared to extrusive rocks. The slow cooling and solidification process of intrusive rocks gives enough time for individual mineral crystals to grow and develop larger sizes. In contrast, the rapid cooling of lava in extrusive rocks does not provide sufficient time for the crystals to grow large, resulting in smaller crystal sizes or even lack of visible crystals in some cases.
Therefore, when examining an igneous rock, observing the size of the crystals within the rock can give a clue about whether it is intrusive or extrusive. Larger crystals are indicative of an intrusive rock, while smaller or absence of crystals often indicates an extrusive rock.