Aim: What are Igneous Rocks? I. Rocks – made up of more than one mineral. Rocks are classified according to how they were formed. Igneous, sedimentary, metamorphic. A. Igneous – rocks that form from magma (lava) when it cools and hardens. • Magma – hot, molten rock. • Lava – magma that reaches earth’s surface. • 3. Rate of cooling can be determined by crystal size.
Large crystals – magma cooled slowly inside earth. Intrusive or plutonic rocks. • Small crystals – lava cools quickly on surface of earth. Extrusive or volcanic rocks. 4. Igneous rocks are classified according to crystal size and color. (go to page 6 of Reference Tables)
Felsic rocks – light in color, low in density, and rich in feldspar and silica. • Mafic rocks – dark colored, high in density, and rich in magnesium and iron. Questions • According to the E.S.R.T.’s, which of these is a fine-grained, dark colored igneous rock? a) basalt b) diorite c) shale d) granite • Large crystals in a rock show that the rock formed by:
Sand collected from a beach contains a mixture of pyroxene, olivine, hornblende, and plagioclase feldspar. According to the E.S.R.T.’s, what can we conclude about the rock that it came from? • a) it was mafic in composition b) it was relatively low in density c) it contained only light-colored minerals d) it was either granite or rhyolite. • 4. According to the E.S.R.T.’s, what is the approximate percentage of plagioclase feldspar in igneous diorite? a) 10% b) 30% c) 60% d) 90%
5. Which characteristic of an igneous rock provides the most information about how it formed? a) Color b) texture c) streak d) hardness
Turn to Page 6 ESRT!!! http://www.eram.k12.ny.us/education/sctemp/190b1c88a4f2b19bc1aff975efb87c7c/igneous.swf