IGNEOUS ROCKS

SILICATE MATERIAL - ALSO CONTAINING GASES -MELTS AT DEPTH

MELTED MAGMA IS LESS DENSE THAN SOLID FROM WHICH IT MELTED AND SO RISES

IF IT SOLIDIFIES ("CRYSTALLIZES", "FREEZES") AT DEPTH IT IS CALLED AN INTRUSIVE ROCK

IF IT ERUPTS AT THE SURFACE IT IS CALLED LAVA AND FORMS AN EXTRUSIVE ROCK. AS THE LAVA COOLS

THE GASES ARE RELEASED INTO THE ATMOSPHERE

IGNEOUS ROCKS CLASSIFIED BY THEIR CHEMICAL COMPOSITION (HOW MUCH SiO2 ), MINERALS, AND WHETHER INTRUSIVE OR EXTRUSIVE

(USGS)