Rocks Rocks are a combination of minerals that are bonded together in some way. • All rocks are made of minerals – Monomineralic- contain one mineral Polymineralic- contain more than one mineral Rocks are classified into three groups by how they are formed Types of Rocks Igneous Sedimentary Metamorphic 3 types of Rocks Types of Rocks Igneous Sedimentary Igneous Rocks: Form from molten rock that cools and hardens. •Sedimentary Rocks: Form from sediments (pieces of other rocks) that are cemented together. Rocks are classified by how they form Metamorphic •Metamorphic Rocks: are formed when old rocks change by heat and pressure. Classification of igneous rocks2 types Intrusive • Form from magma • Cooled and solidified (hardened) slowly deep underground • Large crystal size Extrusive • Form from lava • Cooled and hardened quickly at or near the surface of the earth. • Small or no crystals Igneous rocks are also formed when volcanoes erupt, causing the magma to rise above the earth's surface. Types of igneous rocks • Granite- most abundant igneous rock • Can be made up of feldspar, quartz, mica, and hornblende Obsidian • • Obsidian rocks are igneous rocks that form when lava cools quickly above ground. • Obsidian is actually glass and not a mixture of minerals. The edges of this rock are very sharp. Pumice • Pumice rocks are igneous rocks which were formed when lava cooled quickly above ground. • This rock is so light, that many pumice rocks will actually float in water. • Pumice is actually a kind of glass and not a mixture of minerals. • Extrusive Intrusive Can be: • Felsic: light colored rocks that are rich in elements such as aluminum, silicon. Lower density • Mafic: dark colored rocks that are rich in iron and Mg. Higher density • Coarse-grained texture: takes longer to cool, larger visible mineral crystals • Fine-grained texture: cools quickly with small mineral crystals • Glassy Texture: cools the quickest, no mineral crystals form • Vesicular texture: Gas pockets (holes) • (note) Texture refers to the size/appearance of the minerals ï‚£Fragments of rock get broken down into sediments ï‚£Sediments are transported, compacted, and cemented into rock 1. ARE USUALLY FORMED IN A WATERY ENVIRONMENT. 2. OFTEN LAYERED 3. ARE THE ONLY ROCKS THAT CONTAIN FOSSILS Fossil formation http://www.classzone.com/books/earth_science/terc/conte nt/visualizations/es2901/es2901page01.cfm Clastic Rocks – fragments cemented together and include the sediments: sand, silt, clay, pebbles, and boulders • Generally these rocks are formed from one mineral Rock salt (halite) Rock gypsum- made from gypsum Bituminous coal- fossil fuel Formed from plant remains in Swampy areas- most are millions Of years old Limestone- made from Mineral calcite and Fragments of shells 3. Metamorphic rocks Metamorphic rocks are rocks that have "morphed" into another kind of rock. These rocks were once igneous or sedimentary rocks. The rocks are under tons and tons of pressure, which fosters heat build up, and this causes them to change. How are they formed? • Metamorphic rocks are pre-existing rocks that have been changed by heat and/or pressure without melting. • These pre-existing rocks are called parent rocks Classification- 2 groups • Foliated • Mineral crystals are aligned, or arranged in bands or layers. • Banding: High grade metamorphism. Alternating layers of dark and light minerals. • Non-foliated • Mineral crystals do not have mineral crystals arranged in bands of layers. Example marble and quartzite. Metamorphism • Regional Metamorphism – Caused by extreme pressure and heat. – Happens over wide “regions”. • Contact Metamorphism – Caused by contact with extreme heat. Holey schist! Rock Cycle • Rock must go through melting and solidification to become an igneous rock • Rock must go through weathering and erosion to become sedimentary rock • Rock must go through heat and pressure to become a metamorphic rock Any Questions?
