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Physical Properties of Minerals

Physical Properties of Minerals. How to identify common minerals. What is a mineral? . A mineral is a naturally occuring, inorganic solid with an orderly internal arrangement of atoms (called crystalline structure) and a definite, but not fixed chemical composition.

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Physical Properties of Minerals

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  1. Physical Properties of Minerals How to identify common minerals

  2. What is a mineral? • A mineral is a naturally occuring, inorganic solid with an orderly internal arrangement of atoms (called crystalline structure) and a definite, but not fixed chemical composition. • Minerals, especially gems and precious metals, are among the oldest objects used an treasured by society. • Example 1: Hematite  Metal Iron • Example 2: Gypsum Drywall

  3. Optical Properties: Luster • Luster describes the manner in which light is reflected from the surface of a mineral • Any mineral that shines with a metallic-like appearance has a metallic luster. • Those minerals that do note have a metallic luster are termed nonmetallic and may have one of a variety of lusters which include vitreous, pearly, or earthy.

  4. Example of Luster • Metallic Luster Pyrite, commonly known as fools gold • Nonmetallic Luster (Earthy) Limonite, commonly known as iron ore

  5. Optical Properties: Light Transmission • Opaque: The mineral does not transmit any light. • Translucent: The mineral transmits light, but not an image. • Transparent: An image is visible through the mineral.

  6. Hardness: The Mohs Scale • Hardness, one of the most useful diagnostic properties of a mineral, is a measure of the resistance of a mineral to abrasion or scratching. • A harder substance with scratch or cut into a softer substance. • The Mohs scale, developed by the German mineralogist Friedrich Mohs, rates mineral hardness on a 10 point scale. • 1 = softest mineral in the set • 10= hardest mineral in the set

  7. Streak • The streak of a mineral is the color of fine powder of a mineral obtained by rubbing a corner across a piece of unglazed porcelain– called a streak plate. • The streak of a mineral is unique to the mineral where the color of a mineral may vary. • Hematite (left) may look black, but it will always produce a RED/BROWN streak on a streak plate. • Pyrite (right)looks yellow-gold in the crystal form, but gives a GRAY streak when the plate is used.

  8. Crystal Form • Crystal form is the external appearance or shape of a mineral that results from the internal, orderly arrangement of atoms. • In nature, minerals must compete for space and the result is a dense intergrown mass in which crystals do not exhibit their crystal form.

  9. Cleavage and Fracture • Cleavage is the tendency of some minerals to break along regular planes of weak bonding between atoms in the internal crystalline structure. • When a mineral is broken the flat smooth surfaces of the mineral are called cleavage planes. • Cleavage is determined by noting the number of directions of cleavage and the angles at which the directions of cleavage meet.

  10. Minerals that do not exhibit cleavage when broken are said to fracture. • Fracturing can be irregular, splintery or conchoidal .

  11. Other Properties of Minerals • Magnetism- magnetite (lodestone) • Taste- halite has a salty taste • Feel- talc has a “soapy” feel while graphite feels “greasy” • Striations- feldspar minerals • Reactions to dilute Hydrochloric Acid- carbonate minerals effervesce due to the release of carbon dioxide

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