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Mineral Criteria

This overview explores the defining criteria and classifications of minerals, focusing on their inorganic nature, natural occurrence, crystallinity, and consistent chemical composition. Key mineral classes include silicates and nonsilicates, with further subdivisions such as carbonates and sulfides. Identification methods such as color, streak, luster, hardness using Mohs scale, and cleavage versus fracture techniques are discussed. Special properties like fluorescence, magnetism, and radioactivity highlight the unique characteristics of certain minerals, enhancing our understanding of their identification and classification.

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Mineral Criteria

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  1. Mineral Criteria • Inorganic: not made up of living things • Naturally Occurring: exist in nature • Crystalline Solid: regularly repeating crystalline structure • Consistent Chemical Composition: consistent, no variety

  2. Mineral Classes • Silicates: contain silicon (Si) and oxygen (O) • Nonsilicates: do not contain silicon (Si) and oxygen (O), 6 major groups • Carbonates, Halides, Native elements, Oxides, Sulfates, Sulfides

  3. Mineral Identification • Color: easy to observe, minerals vary in color. • Many minerals are similar in color. • Small amounts of certain elements may greatly affect the color of a mineral. • Weathered surfaces may hide the color of minerals. • Examine freshly exposed surfaces.

  4. Gold

  5. We’re going streaking! • Streak: color of the mineral in powdered form. • Rub a mineral against a piece of unglazed ceramic tile (streak plate). • The streak’s color may differ from the color of the mineral itself.

  6. My precious • Luster: light that is reflected from a mineral’s surface. • Metallic: reflects light similar to polished metal. • Nonmetallic: All other minerals. • Glassy, waxy, pearly, brilliant, and dull or earthy.

  7. Galena

  8. Hey, Mohs! Why I awtah… • Mohs hardness scale: standard scale against which the hardness of minerals is rated. (1-10) • 1 is soft, 10 is hard • The bonds between the atoms that make up a mineral’s internal structure determines the hardness of that mineral. • Test the hardness by scratching the minerals. • p. 111 Mohs Hardness Scale

  9. Gypsum & Talc

  10. Diamond

  11. Cut! • Cleavage: tendency of a mineral to split along specific planes of weakness to form smooth, flat surfaces. • Break along flat surfaces that generally run parallel to planes of weakness in the crystal structure.

  12. Quartz

  13. Acanthite

  14. Time for a Break! • Fracture: break unevenly into pieces that have curved or irregular surfaces. • Uneven or irregular fracture: rough surface • Splintery or fibrous fracture: looks like a piece of broken wood. • Conchoidal fractures: curved surfaces.

  15. Asbestos

  16. Tiptopite (clear) Montgomeryite

  17. Not again! • Density: ratio of the mass to the volume of a substance. D=m/v • Depends on the kinds of atoms that the mineral has and depends on how closely the atoms are packed. • Heavy metals have larger densities. • Helps identifying heavier minerals easier.

  18. Special Properties • Fluorescence: glow under ultraviolet light. • Phosphorescence: continue to glow after ultraviolet light is removed. • Magnetism: attract metal, contain iron. • Radioactivity: nuclei of some atoms are unstable. • Results in nuclei decay over time.

  19. Magnetite

  20. Lights, Camera, Action! • Light rays bend as they pass through transparent minerals. • Double Refraction: Light rays are split into 2 parts as they enter the crystal. • Produces a double image.

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