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Chapter 4

Chapter 4. Minerals. What is a Mineral?. A mineral is a naturally occurring inorganic solid, that has a crystal structure and a definite chemical composition. General Facts About Minerals. 2,000 + minerals have been identified

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Chapter 4

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  1. Chapter 4 Minerals

  2. What is a Mineral? • A mineral is a naturally occurring inorganic solid, that has a crystal structure and a definite chemical composition

  3. General Facts About Minerals 2,000 + minerals have been identified • A few are “native elements” -- made of only one element, such as sulfur, gold. copper, and graphite (carbon) • Most are compounds, especially the silicate group (Si, O). • Other important groups are oxides, carbonates, and sulfides.

  4. Naturally Occurring: • Formed by process in natural world (ex: magma cooling) • Not man made

  5. Inorganic • NOT from materials living or once living (ex: coal & oil are not minerals)

  6. Solid: • definite volume and shape

  7. Crystal Structure: • particles line up in repeating patterns • has flat side called faces (ex: halite is cubic) see pg 3 in notes

  8. Definite Chemical Composition: • always contains certain elements in definite proportions • Minerals are compounds Quartz – SiO4 Halite -NaCl • Minerals are elements Gold (Au), Silver (Ag), Copper (Cu)

  9. Minerals can have the same chemical composition (Carbon) but different physical properties because of their crystal structure DiamondGraphite

  10. Identifying Minerals Geologist have identified approximately 3800 minerals. Each mineral has characteristic properties that can be used to identify it.

  11. COLOR: The color of a mineral can be easily observed. But color alone often provides too little information to make an identification.

  12. Gold, Pyrite, and Chalcopyrite can all appear gold in color but only one is the real valuable mineral.

  13. Some Colors of Quartz

  14. STREAK: The streak of a mineral is the color of its powder. Streak can be observed by rubbing a mineral against an unglazed porcelain tile.

  15. The color of a mineral may vary but its streak does not. The streak and color are often different. For example, pyrite is gold in color but produces a greenishblack streak. gold gold streak pyrite greenish black streak

  16. LUSTER: Luster is used to describe how light is reflected from the mineral’s surface.

  17. Some words used to describe luster might include: • Metallic – looks like a metal or shiny like a metal (galena)

  18. Examples of metallic luster

  19. Submetallic – dull, looks like “unshiny” metal (graphite)

  20. Glassy or vitreous – shines like glass (topaz)

  21. Earthy, dull or chalky – does not reflect much light (hematite or limonite)

  22. Waxy, greasy or pearly – has a muted shine; may resemble shells or pearls (talc)

  23. DENSITY: A mineral will have a definite density regardless of the size of the mineral sample. The equation for density is: D = M V Density = Mass divided by volume

  24. CRYSTAL SYSTEMS: Crystals of minerals grow atom by atom.

  25. The most common crystalline structure • Silica-oxygen tetrahedron – basic building block for silicate minerals

  26. Geologists classify these structures into six groups based upon the number of crystal faces.

  27. Sometimes, the crystal structure is obvious from the mineral’s appearance.

  28. Crystals that grow in open spaces can form almost perfectly.

  29. But, ones that grow in tight spaces are often incompletely formed. The crystal structure is visible only under a microscope.

  30. CLEAVAGE or FRACTURE: The way a mineral breaks apart can help identify it.

  31. A mineral that splits along flat surfaces has the property of cleavage.

  32. Cleavage depends upon how the atoms in the crystal system are arranged. The crystals will tend to break apart (or cleave) where the chemical bond (or attraction) between atoms is weakest.

  33. Cubic cleavage of fluorite and halite FLUORITE HALITE

  34. Cleavage MUSCOVITE BIOTITE

  35. Fracture describes how a mineral looks when it breaks in an irregular way.

  36. A variety of terms are used to describe fracture. Quartz breaks in a curve or shell like shape (aka conchoidal)

  37. Copper and iron may form jagged points.

  38. Some minerals crumble. Minerals that from irregular surfaces have uneven fracture

  39. HARDNESS: Mineral hardness is its resistance to being scratched. A mineral can be scratched by any other mineral that is harder than it is.

  40. The Moh’s hardness scale is use to describe mineral hardness. This scale ranks 10 minerals from softest to hardest.

  41. SPECIAL PROPERTIES: Some mineral exhibit special properties that are unique. These might include:

  42. Fluorescence – glows under an ultraviolet light (fluorite)

  43. Phosphorescence – ability to glow after ultraviolet light is removed.

  44. Magnetism – acts like a magnet, attracts iron (magnetite)

  45. Optical Properties: bends light to produce double image (aka double refraction) (calcite)

  46. Reactivity – reacts to an acid, effervescence(aragonite, calcite)

  47. Odor – very distinctive scent (sulfur)

  48. Taste - very distinctive flavor (halite –salty)

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