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Minerals and Rocks Based on Discover God’s Creation Chapter 8-1, 2 & 3 By Rebecca K. Fraker Matter • Matter is anything is anything—solid, liquid, or gas—that has mass and takes up space. • Matter on earth is made up of one or more of the 92 naturally occurring atoms or elements, substances that normally do not change into other substances. Elements • Each element has special properties that identify it. • While elements do not change, they can combine with others to form compounds. • When hydrogen and oxygen combine they form a common compound –water. Other examples of compounds: Minerals • Minerals are elements or compounds that occur in Earth. • Gold, silver, and copper are singleelement minerals. Minerals • Most minerals, however, are compounds made up of two or more elements. • Table salt is made of sodium and chlorine. plus salt Sodium Chlorine All minerals share four features: • They occur naturally in the environment. • The do not come from living things. • Each has unique properties and composition. • Their atoms are arranged in an orderly pattern. How are minerals found? • Minerals are often found in concentrated deposits. • Some minerals, such as quartz and feldspar, form as magma cools in the cavities or cracks in the crust. • Heavy minerals, such as gold, are deposited as water washes them into rivers and they settle to the bottom. Other Minerals • Still other minerals, such as gypsum and halite (rock salt) form as the water they are dissolved in evaporates from shallow lakes. Identifying Minerals • How do you tell the difference between fool’s gold and real gold? • Geologists use several tests to identify the properties of minerals. Hardness Test • The Mohs’ scale indicates the hardness of a mineral. It is based on 10 minerals. Number 1 is the softest, and Number 10 is the hardest. • A mineral is tested by seeing which other minerals it will scratch. If it scratches 1,2,and 3, it has a hardness of 4. • Diamond has a hardness of 10 and can scratch all other minerals. Mohs’ Scale • An easy way to test hardness is to use your fingernail, a penny, a knife blade, and glass. Fingernail=1 Copper penny=3 Knife blade=6 Glass=8 Streak Test • Some minerals are identified by their color. • Sulfur, for example, is bright yellow. • When the color of a mineral is hidden by dirt, you can do a streak test by rubbing the mineral across a rough piece of tile or a metal file. • The color of the streak helps identify it. • Fool’s gold leaves a dark-green streak. • Real gold leaves a golden streak. Luster Test • Luster refers to how a mineral reflects light. • A mineral can have a metallic or nonmetallic luster. • Galena, which shines like a piece of metal, has a metallic luster. • Quartz has a nonmetallic luster because ti is glassy, waxy, or dull in appearance. Crystal-Shape test • The crystals of each mineral have a specific shape. • Salt crystals are always shaped like a cube. • If you can see the shape of a crystal, you can identify the mineral. But that is not always easy. Salt Crystals sulfur feldspar amythest Cleavage/Fracture Test • If a mineral is hit hard enough, it will break or fracture. • Some minerals, like fool’s gold, break unevenly. • Others, such as mica, split into thin sheets. This quality is called cleavage. Other tests • A few minerals contain iron and are attracted by a magnet. • Some minerals contain carbonates that bubble and fizz when acid touches them. • Rock salt (halite) can be identified by its taste, while sulfur when scratched gives off a rotten eggs smell. Other tests • Calcite splits light into two beams that form a double image. • Some minerals are fluorescent. They normally look dull, but are bright and colorful under ultraviolet light. Metals • Minerals such as gold, copper, and aluminum are metals • They have luster and can be hammered into flat sheets or drawn into a wire. • Metals are good conductors of heat and electricity. Because of these qualities, they are widely used. Mineral or Rock? • Minerals are single elements or combinations of elements. • Rocks are mixtures of various minerals. • In mixtures, ingredients do not chemically combine and change; they simply stick together. Rocks • Concrete and granite provide examples that demonstrate such mixtures. • Rocks are often identified by the minerals that stick together to form them. • Concrete is sand, cement, and water mixed together. It then is poured into a shape and hardens. Granite • Granite is a common rock used for buildings, monuments, and counter tops. • Feldspar is the light-colored part of granite, quartz makes up the clear crystals, and biotite and mica are the darkcolored specks.