Mrs. Barnes 3rd Grade Science Class Igneous Rocks Mrs. Barnes 3rd Grade Science Class

What is an igneous rock Igneous rocks are formed from melted rock that has cooled and solidified. When rocks are buried deep within the Earth, they melt because of the high pressure and temperature; the molten rock (called magma) can then flow upward or even be erupted from a volcano onto the Earth's surface. When magma cools slowly, usually at depths of thousands of feet, crystals grow from the molten liquid, and a coarse-grained rock forms. When magma cools rapidly, usually at or near the Earth's surface, the crystals are extremely small, and a fine-grained rock results.

Igneous Rock Continued A wide variety of rocks are formed by different cooling rates and different chemical compositions of the original magma. Obsidian (volcanic glass), granite, basalt, and andesite porphyry are four of the many types of igneous rock. 

Gabbro is a coarse-grained, dark-colored, intrusive igneous rocks Gabbro is a coarse-grained, dark-colored, intrusive igneous rocks. It is usually black or dark green in color and composed mainly of the minerals plagioclase and augite. It is the most abundant rock in the deep oceanic crust.

Granite Granite forms when bits of quartz and feldspar are shot out of volcanoes, so its one kind of igneous rock.

Obsidian is an igneous rock that forms when molten rock cools very rapidly. The result is a rock that cooled so fast, crystals did not get a chance to form. Obsidian is a volcanic glass with a smooth and uniform structure.

Diorite Diorite is the name used for a group of coarse-grained igneous rock with a composition between that of granite and basalt. These often form above a convergent plate boundary where an oceanic plate sub ducts beneath a continental plate.