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Rocks and Minerals Part 1: Minerals What Is A Mineral? To be classified as mineral, a substance must: 1. Be a solid 2. Be formed naturally 3. Be inorganic (not from living things) 4. Have a crystal structure 5. Have a fixed chemical composition Examples Mineral… or not? Mineral NOT! Not a solid. Examples Mineral… or not? Mineral NOT! Not formed naturally. Examples Mineral… or not? Mineral NOT! Not inorganic. Examples Mineral… or not? Mineral NOT! Not inorganic. Examples Mineral… or not? NOT! NoNot crystal inorganic. structure. Mineral Examples Mineral… or not? NOT! No fixed composition. Mineral Review To be classified as mineral, a substance must: 1. Be a solid 2. Be formed naturally 3. Be inorganic (not from living things) 4. Have a crystal structure 5. Have a fixed chemical composition A Huge Variety… Identifying Minerals Minerals are identified using 7 key characteristics: Color Crystal Shape Luster Cleavage / Fracture Streak Special Properties Hardness 1. Color Color is an easy property to judge. The problem with color is that it can only be used to identify minerals with their own unique and specific color. For example, all the minerals shown are quartz! 2. Luster Luster is how the mineral reflects light. The 2 basic types of luster are: Metallic Non-Metallic Non-metallic can be further divided into: Silky, greasy, waxy, earthy, dull 3. Streak Streak is the color of its powder. It is found by rubbing the mineral on a piece of porcelain called a streak plate This causes tiny pieces of the mineral to rub off, which reflects its true color 4. Hardness Hardness is how hard it is to scratch a mineral. Hardness in measured using Moh’s Hardness Scale (1872). Harder minerals (diamond) scratch softer minerals (talc) and receive a higher rating. Moh’s Hardness Scale Hardest Softest 10. Diamond 09. Corunudum 08. Topaz 07. Quartz 06. Orthoclase 05. Apatite 04. Fluorite 03. Calcite 02. Gypsum 01. Talc 5.5 Glass 4.5 Iron Nail 3.5 Penny 2.5 Fingernail 5. Crystal Shape Crystals form in certain geometric shapes which can be used to identify them. Cubic Trigonal Tetragonal Monoclinic Hexagonal Triclinic Galena (cubic) Diamond (trigonal) Quartz (tetragonal) Wulfenite (monoclinic) Garnet (hexagonal) Axinite (triclinic) 6. Cleavage or Fracture When struck, minerals split in certain ways. Cleavage is when a mineral splits easily along flat surfaces Fracture is when a mineral breaks apart in an irregular way Cleavage vs. Fracture Calcite (cleavage) Quartz (fracture) 7. Special Properties Some minerals have their own unique properties. Sulfur smells like rotten eggs. Magnetite is naturally magnetic. Halite tastes salty (because it’s salt!) Review Minerals are identified using 7 key characteristics: Color Crystal Shape Luster Cleavage / Fracture Streak Special Properties Hardness Common Minerals Calcite Barite Common Minerals Fluorite Gypsum Gem Minerals Tourmaline Opal Gem Minerals Beryl (Aquamarine) Diamond Metallic Minerals Pyrite (on Sphalerite) Gold Metallic Minerals Malachite (copper ore) Malachite (cross section) Colorful Minerals Azurite Vanadinite Colorful Minerals Tourmaline Cavansite Any Questions? Rocks and Minerals Part 2: Rocks Types of Rocks There are three major types of rocks: Igneous Metamorphic Sedimentary Igneous Rocks Igneous comes from the Latin word for “fire”. Igneous rocks form from the cooling of molten rock called magma or lava. Igneous rocks fall under 2 broad categories: Intrusive Rocks Extrusive Rocks Rocks formed beneath the Earth. Rocks formed at the Earth’s surface. Intrusive Igneous Rocks Intrusive igneous rocks form below the Earth’s surface as magma cools and hardens. Intrusive Igneous Rocks Intrusive rocks have large crystals. It is warm below the Earth. Hot magma cools down slowly. Minerals have lots of time to combine together. This forms coarse-grained rocks with large crystals. Granite Extrusive Igneous Rocks Extrusive igneous rocks form above the Earth’s surface as lava cools and hardens. Extrusive Igneous Rocks Extrusive rocks have small crystals. It is cooler at the surface. Hot lava cools down quickly. Minerals do not have a lot of time to come together. Basalt This forms fine-grained rocks with small crystals. Extrusive Igneous Rocks Some extrusive rocks are formed in mid-air! Frothy lava is shot into the air and cools down rapidly, trapping gas bubbles inside it. Scoria Scoria & pumice are examples. Both are full of tiny holes and are very light! Pumice Extrusive Igneous Rocks Scoria and pumice are formed here. Extrusive Igneous Rocks One extrusive rock is formed near water. Water is cold. Hot lava cools instantaneously. There is NO time for minerals to combine together. This forms glassy rocks with no crystals. Obsidian Extrusive Igneous Rocks Obsidian is formed here. Sedimentary Rocks Sedimentary rocks are formed from sediments. Sediments are small pieces of material that come from rocks or living things. There are 6 kinds of sediments: shells gravel cobbles sand pebbles silt or clay Types of Sediments Largest shells cobbles pebbles gravel sand Smallest silt / clay Formation of Sedimentary Rock Sedimentary rocks are formed through a series of processes. 1. Erosion Running water, wind or ice loosen and carry away sediments. Formation of Sedimentary Rock Sedimentary rocks are formed through a series of processes. 2.1.Deposition Erosion The sediments settle Running water, out or of the wind ice water loosen or wind carrying and carry away it and form layers. sediments . Formation of Sedimentary Rock Sedimentary rocks are formed through a series of processes. 3.1. Compaction 2. Deposition Erosion Over time, water, layers The sediments settle Running build on top, out of the wind orwater ice the orpressing wind carrying loosen and carry it and formtogether layers. . sediments away sediments. Formation of Sedimentary Rock Sedimentary rocks are formed through a series of processes. 4.1. Cementation 3. 2. Compaction Deposition Erosion The sediments settle During Over time, compaction, layers Running water, out of the minerals build on crystallize top, wind orwater ice orpressing windtogether carrying and bind the to loosen and carry form rock. it and form layers.. sediments together away sediments. Sedimentary Rock Sedimentary rocks differ by particle size. Shale is made from clay and silt grains that settle on the bottom of a river and are cemented together. Sandstone is made when larger sand grains are cemented together. Sedimentary Rock Sedimentary rocks differ by particle size. Conglomerate is made from rounded pebbles cemented between grains of sand and gravel. Breccia is made from angular cobbles cemented between clay and sand grains. Sedimentary Rock Sedimentary rocks differ by particle size. Limestone is made from shells of marine organisms that have been crushed and cemented together. Coal is made from swamp plants buried in water and compressed over millions of years. Review Largest shells limestone cobbles breccia pebbles sand conglomerat e conglomerat e sandstone silt / clay shale gravel Smallest Metamorphic Rock Metamorph means to “change form”. Metamorphic rocks are made when other rocks are changed by heat and pressure in the Earth. This causes the rock to change in: appearance texture crystal structure mineral content Two Categories There are 2 main types of metamorphic rock. Foliated Non-foliated Foliated rocks have minerals arranged in layers or bands. Non-foliated rocks have minerals arranged randomly. slate, gneiss marble, quartzite Metamorphic Rock Metamorphic rock comes from existing rocks. Shale becomes Slate Sandstone becomes Quartz Metamorphic Rock Metamorphic rock comes from existing rocks. Granite becomes Gneiss Limestone becomes Marble Any Questions? Rocks and Minerals Part 3: The Rock Cycle The Rock Cycle Rocks are destroyed and reformed continuously. The rock cycle is a series of processes on Earth that change rocks from one form to another. Some of the changes are fast, like in a volcanic eruption. Some of the changes are slow, like weathering and erosion. Melting Liquid Magma Metamorphic Rock Heat & Pressure Sedimentary Rock Cooling Igneous Rock Deposition Compaction Cementation Weathering Loose Sediments Any Questions?