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Unit D Chapter 2 “Rocks and the Rock Cycle” Lesson 1 Pgs D40-D45 Minerals Minerals are the building blocks of rocks. A Mineral is a natural solid substance that has a definite chemical composition and physical structure. There are more than 4000 minerals, but only about a dozen are common. Minerals make up most of the rock in earth’s crust. Quartz is one of the most common rock forming minerals. Combined with feldspar, it makes granite, the most common rock on earth. Some people believe (not kidding) that quartz balances your physical, mental, emotional, and spiritual planes. Not only that, but can enhance your organs, memory and even psychic ability! In reality land, your are just holding a rock. Minerals Scientists identify minerals by their properties. Some of the properties are hardness, color, crystal shape, density, and the color it leaves when scraped on tile. Diamonds are the hardest minerals on the planet. The Hope Diamond is a blue diamond weighing at 45.52 carats. Chalk is a very soft mineral and very common. Formation of Igneous Rocks Melted rock within the Earth’s mantle is called magma. Igneous rock is formed when magma pushes up through the crust and hardens into rock. Magma that reaches the surface is called lava. There are two types of igneous rock; intrusive and extrusive. If this is your view of lava, consider taking a few steps back. Intrusive Igneous Rock Intrusive Rock is formed when magma hardens inside Earth’s crust. Intrusive rock is also sometimes called plutonic rock after Pluto, the Greek god of the underworld. (Before you yell out “It was Hades!!” I’ll explain.) These intrusive rocks can be called Plutons. Granite is an intrusive rock. The granite boulders in Elephant Rocks State Park are a great place to see plutonic rock. Intrusive Igneous Rock Intrusive rocks cool slowly because they form underground. This gives crystals longer to form so intrusive rocks typically have large crystals. Large plutons that get exposed by erosion are called batholiths. They can be as large as mountains. This batholith is called Shiprock in New Mexico. It is the hardened core of an extinct volcano. The rest of the volcano eroded away, leaving the hardened magma behind. Extrusive Igneous Rocks Extrusive Rock is formed when lava cools quickly on Earth’s surface. Because they cool quickly, crystals do not have much time to form. Because of this, extrusive rocks have a fine-grained texture. Some examples of extrusive rock include obsidian and pumice Pumice forms with millions of bubbles making it so light, that it is the only rock that can float! Obsidian forms as a black, volcanic glass. Uses of Igneous Rocks Because igneous rocks are some of the most common on Earth, they are used in many things. Granite is a strong, durable rock used for building materials. The Empire State Building and The Great Wall of China are made from granite. Uses of Igneous Rocks Obsidian has been used for tools and jewelry. Obsidian breaks with a sharp edge and was used for cutting tools. Pumice is ground into a powder for scouring substances in soaps and powders. It was even used as a tooth cleaner but had the side effect of filing down the teeth to little nubs. Uses of Igneous Rocks Igneous rocks are also sources of valuable ores. Ores are useful minerals or mixtures of minerals that are mined. These ores contain chromium, platinum, diamond, nickel and copper. Platinum in its raw form. Real diamond ore. Not so real diamond ore.