Intrusive rocks

Part of Hall of Planet Earth.

Intrusive rocks

Magma is molten rock. As the mantle or crust melts, magma separates from the solid rock, rises through cracks, and collects to form chambers of varying sizes. Frequently, it reaches the surface to erupt as lava from volcanoes. But many large bodies of magma never get that far. Instead, they solidify in the crust to form intrusive rocks. There is an enormous variety of these rocks, and the characteristics of each kind are determined primarily by the composition of the magma and how rapidly it cools and crystallizes.

Structures Formed by Magma_ILL
Rocks of the Stillwater Complex_ILL

In This Section

Exhibit Anorthosite This is an anorthosite, composed almost entirely of plagioclase (white). Exhibit Harzburgite This harzburgite is one of the lowermost layers of the Stillwater Complex. Exhibit Norite This norite is composed of plagioclase (labradorite, white) and orthopyroxene (bronzite, brown). Exhibit Zoned Labradorite This giant labradorite crystal exemplifies the texture that results when anorthosite rocks cool very slowly.