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Mineral Identification Basics: Comparing Silicate and Nonsilicate Crystals

Learn about the basics of mineral identification, including the definition of minerals, the differences between silicate and nonsilicate minerals, and the various physical properties used to distinguish minerals. Discover the six types of silicate crystalline structures and three common nonsilicate crystalline structures. Explore seven physical properties and five special properties that aid in identifying different minerals.

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Mineral Identification Basics: Comparing Silicate and Nonsilicate Crystals

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  1. Objectives • Definemineral and Comparethe two main groups • Identifythe six types of silicate crystalline structures. • Describethree common nonsilicate crystalline structures. • Describeseven physical properties that help distinguish one mineral from another. • Listfive special properties that may help identify certain minerals.

  2. Mineral Identification Basics • Mineral: a solid with an orderly internal structure • To be a mineral, a substance must have 4 characteristics: • must be inorganic—not made of living things • must occur naturally—not man-made • must be a crystalline solid • must have a consistent chemical composition Cubic Fluorite Crystal

  3. Characteristics of Minerals The diagram below shows the 4 characteristics of minerals

  4. Silicate Minerals • All minerals can be classified into two main groups—silicate minerals and nonsilicate minerals • Silicate mineral:a mineral which contains silicon and oxygen, and may contain one or more metals • Common silicate minerals include quartz, feldspars, and micas • Silicate minerals make up 96% of Earth’s crust. Quartz and feldspar alone make up more than 50% of the crust.

  5. Nonsilicate Minerals • Nonsilicate mineral: a mineral that does not contain silicon and oxygen • comprise about 4% of Earth’s crust • organized into six major groups. • Carbonates • Halides • native elements • Oxides • Sulfates • sulfides

  6. Crystalline Structure • Crystal: a solid whose atoms, or molecules are arranged in a regular, repeating pattern • Each mineral has a specific geometric arrangement of atoms, also known as its crystalline structure. • Scientists study the structure of crystals using X rays. These produce an image which shows the geometric arrangement of atoms in the crystal.

  7. Physical Properties of Minerals • Mineralogist: a person who examines, analyzes, and classifies minerals • Each mineral has specific properties, which are the result of its composition and crystalline structure. These properties provide useful clues for identifying minerals. • The 6 properties used to classify minerals are: • Color • Streak • Luster • Cleavage • Fracture • Hardness

  8. Color • Color: most noticeable property, but least-accurate method for identifying a mineral Many minerals have similar colors

  9. Streak • Streak: color of a mineral in powdered form • More reliable than color for mineral identification • Determined by rubbing the mineral against a streak plate  • The streak is often different from the apparent color of an unground sample • The streak color of a mineral will always be the same, even it its external color varies

  10. Most metallic minerals have a dark streak Magnetite Chalcopyrite and Galena Galena Graphite

  11. …while most nonmetals have a light streak Amethyst calcite Peridot (polished) Citrine

  12. Luster • Luster: The quality and intensity of light reflected from the surface of a mineral • Luster is either metallic or nonmetallic

  13. Metallic Luster • Metal-like shine • Dark Streak

  14. Nonmetallic Luster • More common • Light streak color

  15. Cleavage and Fracture • Cleavage: tendency of a mineral to split • Occurs due to weakness in structure of mineral • Fracture: the way a mineral breaks along either curved, or irregular surfaces • Uneven or irregular fractures have rough surfaces. • Curved fractures are smooth

  16. Hardness • Hardness: measure of resistance to scratching • A harder substance will scratch a softer substance • Hardness can be determined by comparing the mineral to those on the Mohs hardness scale -> Mohs Hardness Scale

  17. Magnetism • Magnetism: ability of a mineral to act as a magnet • Most commonly associated with minerals rich in iron • Minerals rich in iron are called magnetites • Iron is highly magnetic…remember this! This is a piece of iron with a magnet attached

  18. Magnetism This is a sample of “black sand” from Lynx Creek, Arizona. Its dark color is due to its high concentration of magnetite. See what happens when a magnet is place beneath the bottom right portion of the paper? This technique is used to separate out much of the unwanted material in the search for gold.

  19. Magnetism Lodestone is a variety of Magnetite which is a natural magnet.

  20. Fluorescence Willemite • A few minerals have some additional, special properties • The ability to glow under ultraviolet light is called fluorescence. • Fluorescent minerals absorb ultraviolet light and then produce visible light of various colors.

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