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Aim: What are the characteristics of minerals and how do we identify them? I. Minerals A. 4 Characteristics 1. Naturally occurring 2. solid materials 3. atoms are arranged in an orderly manner 4. inorganic 5. have a definite chemical composition “NSAID” B. Rock forming minerals – of the 2400 minerals on the earth, about a dozen of them are so abundant that they comprise of more than 90% of the lithosphere. 1. Lithosphere – outer shell of the earth consisting of the crust and uppermost part of mantle. C. Elements in minerals – mineral’s may be composed of single elements or compounds of two or more elements. 1. Most common elements in minerals: a. Oxygen (O) – since it is the most abundant element in earth’s crust by both mass (46.6%) and volume (93.8%). b. Silicon (Si) – 27.7% by mass and 0.9% by volume. c. Aluminum (Al) d. Iron (Fe) e. Calcium (Ca) f. Sodium (Na) g. Potassium (K) h. Magnesium (Mg) Silica Tetrahedron SiO4 – 4 oxygen atoms to every silicon atom animation p. 16 ESRT 1.Color – may be used for mineral identification. Many minerals have the same color. It is NOT the most reliable method of identifying a mineral. Different minerals with the same color 2 Different types of quartz – same mineral, different color. 2. Hardness - the resistance of a mineral to being scratched. If you scratch two minerals together, the harder mineral will scratch the softer one. a. Mohs’ Scale of Hardness - assigns a value of 1 through 10 to a mineral, with “1” being the softest value (talc) and “10” being the hardest value (diamond). 3. Streak – the color of the powder of a mineral when crushed or scratched across a streak plate (piece of unglazed porcelain). A mineral’s color may look different than its streak. Generally, nonmetallic minerals do not leave a streak. What are three ways that we can identify minerals? 4. Luster – the appearance of light reflected from a minerals’ surface. a. Metallic luster – shines like a metal b. nonmetallic luster – might look glassy, waxy, greasy, pearly, earthy, or dull. Nonmetallic Pyrite (Fools Gold) metallic 5. Cleavage – when a mineral breaks along one or more smooth surfaces galena a. Fracture – when minerals do not break along flat planes. Fracture 6. Crystal Structure – a crystal is a regular shaped solid formed by an ordered pattern of atoms. Minerals have characteristic crystals. (Pyrite – calcite) 7. Density a. Specific gravity – Weight of a mineral divided by weight of an equal volume of water. C3S2HL