Bellringer What are five characteristics that make up the definition of a mineral? Quiz Wednesday: Chem – Rock Cycle inorganic Natural solid Set chemical composition Crystalline structure

Igneous Rocks

Granite (rock made of quartz and feldspar) Rocks Rocks – combinations of minerals Rocks are identified by the minerals that make them up Granite (rock made of quartz and feldspar)  Quartz (mineral) Feldspar (mineral) 

Rocks Three main types of rocks, all formed different ways Igneous Sedimentary Metamorphic

Igneous Rocks Igneous rocks – rocks created from the cooling and crystallization of magma or lava Igneous is Latin for “fire” (same root as “ignite”) The most common rocks in Earth’s crust Two main types

Types of Igneous Rocks Intrusive rocks – form from magma that has cooled and crystallized slowly underground Gradual cooling = rocks with larger mineral crystals Intrusive rocks because form INside the Earth Granite—most common intrusive igneous rock (makes up most of the continental crust)

Types of Igneous Rocks Extrusive rocks – form from the rapid cooling and crystallization of lava on Earth’s surface Rapid cooling = no or only small mineral crystals Extrusive rocks form after they EXit Earth’s surface

Extrusive Igneous Rocks Intrusive Igneous Rocks Obsidian (volcanic glass) Rhyolite

Types of Igneous Rocks magma lava slowly quickly large small Type of Rock Intrusive Rocks Extrusive Rocks Form from… Cool… Form _____ grains/crystals magma lava slowly quickly large small

Classifying Igneous Rocks Igneous rocks are classified two ways: 1. Mineral Composition: Felsic – high in SiO2, low in Fe&Mg; light-colored (ex: granite) Intermediate Mafic: low in SiO2, high in Fe & Mg; dark-colored (ex: gabbro) Ultramafic granite gabbro

Classifying Igneous Rocks 2. Mineral Grain Size: large grains (intrusive) or small grains (extrusive)

Classifying Igneous Rocks Mineral grain shapes can be observed by looking at very thin sections under microscopes Many mineral grains have interlocking edges that form as the grains crystallize together Well-shaped crystal grains form during fractional crystallization by floating to the top and having space to grow Thin section of gabbro

Classifying Igneous Rocks Porphyritic texture – igneous rocks with large, well-formed crystals surrounded by finer-grained minerals Indicates a complex cooling history where slowly-cooling magma suddenly began rapidly cooling because it erupted onto Earth’s surface

Uses for Igneous Rocks Building Materials High strength due to interlocking grains Many of the minerals are resistant to weathering Beauty of crystals desired in modern decorating (ex: granite countertops)

Uses for Igneous Rocks Ore Deposits Veins – many valuable metals (gold, silver, lead, copper) are left over at the end of magma crystallization, fill cracks in surrounding rocks, and eventually crystallize to form veins A gold vein

Igneous Rock Lab Get in groups of 2-3 You will need a lab sheet (one per group), laminated directions, and a bag of rocks IGNORE THE SAMPLE NUMBERS Turn in paper when done and return supplies

Work with the same group you did on Friday. Finish your mineral lab Work with the same group you did on Friday. Finish your mineral lab. Follow the numbers in the grid, not on the minerals. When done, begin Igneous Rock Lab. Supplies (Lab paper, Laminated directions, bag of rocks) are by the mineral boxes. IGNORE THE SAMPLE NUMBERS. Turn in paper when done and return supplies.