Descriptive of igneous rocks that have formed
underground. Intrusive, or plutonic, igneous rock forms
when magma is trapped deep inside the Earth.
Great globs of molten rock rise toward the surface. Some of the magma may
feed volcanoes on the Earth's surface, but
most remains trapped below, where it cools very slowly over many thousands
or millions of years until it solidifies. Slow cooling means the individual
mineral grains have a very long time to grow, so they grow to a relatively
large size. Intrusive rocks have a coarse-grained texture. A common intrusive
rock is granite.
|Types and composition of intrusive
Compare with extrusive.
AND PLANETARY SCIENCE