Chapter 4 Section 2

Magma- molten rock material Comes from deep below Earth’s surface Temperature 650 to 1,200 degrees Celsius Generally highly radioactive Less dense than surrounding rock so it is forced upward Reaches Earth surface- called Lava

Formed from magma that cools below the surface Mineral grains are large because the magma cooled so slowly Only reach Earth’s surface if forced upward

Lava that cools on Earth’s surface The lava cools quickly so the mineral grains are small to non-existent. Fine grained minerals

Pumice Obsidian Scoria The lava cooled so quickly that there was not time for orderly arrangement of atoms to occur. Therefore, no crystals Gases are trapped in scoria and pumice that eventually escape causing holes

Intrusive vs extrusive The magma from which they form determines the mineral composition, density, color, and melting temperature

Dense, dark colored Magma is rich in iron and magnesium and poor in silica Flows from the volcanoes in Hawaii making the black beaches Intrusive- gabbro Extrusive- basalt

Light colored Lower density than basaltic rocks Contains silica but lower amounts of iron and magnesium Intrusive- granite Extrusive- rhyolite, obsidian

Mineral composition between basaltic and granitic Volcanoes around the rim of the Pacific Rim form andesitic magma Intrusive- Diorite Extrusive- Andesite