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Minerals

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  1. Minerals

  2. What is a mineral? • A mineral is a naturally occurring, inorganic solid with an orderly crystalline structure and a definite chemical composition

  3. 5 Characteristics of Minerals • 1. Naturally occurring- forms by natural geologic processes, synthetic gems are not considered minerals • 2. Solid Substance- within temperature ranges that occur at Earth’s surface • 3. Orderly crystalline Structure- atoms are arranged in an orderly and repetitive manner • 4. Definite Chemical Composition- minerals are chemical compounds made up of a two or more elements (exception- native elements) • 5. Generally Considered Inorganic- table salt is inorganic, sugar is organic and is not a crystal. Sugar comes from a plant • Calcium carbonate- secreted by marine animals, inorganic or organic?

  4. How do minerals form? • Four major processes by which minerals form • 1. Crystallization from magma • 2. Precipitation • 3. Pressure and Temperature • 4. Hydrothermal Solutions

  5. Crystallization of Magma • Magma is molten rock that occurs deep within the Earth • As magma cools, elements combine to form minerals • First minerals formed are rich in iron, calcium, magnesium • Next are minerals rich in sodium, potassium, and aluminum

  6. Precipitation • Minerals form when water evaporates in lakes, rivers, ponds, and oceans • Minerals are left behind or precipitated from the water • Halite and calcite form this way

  7. Pressure and Temperature • Some minerals from when others are subject to changes in pressure and temperature • Atoms are rearranged to form more compact minerals • Talc and muscovite are formed this way

  8. Hydrothermal Solutions • Hydro (water) thermal (heat) • Very hot mixtures of water and dissolved substances • Can have temperature between 100oC and 300oC • Chemical reactions occur at these temperatures causing minerals to form, or as solution cools minerals form

  9. Mineral Groups • There are over 3800 named minerals on Earth and more are identified each year • Common Minerals are classified into groups based on their composition • Seven mineral groups- • Silicates, carbonates, oxides, sulfates, sulfides, halides, native elements

  10. Silicates • These are the most common- remember from chemistry unit, the most abundant elements in Earth’s crust are oxygen and silicon • Silicon-oxygen tetrahedron- structure which consists of one silicon to four oxygen molecules (most silicates occur in this form) • Most silicate minerals form from crystallization of magma near or far below earth’s surface • Examples include- quartz, augite, micas

  11. Carbonates • Second most abundant mineral group • Contain carbon, oxygen, and one or more other metallic elements • Examples include calcite, dolomite, limestone, marble

  12. Oxides • Oxides contain oxygen and one or more other elements, which are usually metals • Some form under Earth’s surface from crystallization of magma (rutile), others from when minerals are subject to changes in temperature and pressure (corundum), others form when a mineral is exposed to liquid water (hematite, iron oxide)

  13. Sulfates and Sulfides • Both contain sulfur • Sulfates- (anhydrite, and gypsum) form when mineral rich waters evaporate • Sulfides- (galena, sphalerite, pyrite) form from hydrothermal solutions

  14. Halides • This group contains a halogen ion plus one or more other elements • Halogens occur in group 17 (7a) of the periodic table • Examples include- halite and fluorite

  15. Native Elements • This group occurs in pure elemental form • Examples include- gold, silver, copper, sulfur, carbon (graphite and diamonds)

  16. Properties of Minerals and Mineral Identification • Properties of minerals are determined by composition and structure • Color • Streak • Luster • Crystal Form • Hardness • Cleavage • Fracture • Density • Unique properties include- magnetism, double refraction, chemical reactions with HCl

  17. Color and Luster • Color can be unique to some minerals, but for most it is not the most useful for identification • Color within minerals can vary depending on other elements present within the mineral • Luster- how light is reflected from the surface of a mineral • Metallic (metal like), vitreous/glassy (quartz), pearly, silky, earthy

  18. Streak and Crystal Form • Color of a mineral in its powdered form • We can use a streak plate (a sheet of unglazed porcelain) to determine this property • Crystal form- visible expression of internal arrangement of atoms • When a mineral forms without any space restrictions it will develop into a perfect crystal with well developed faces • 6 Crystal Forms

  19. Type 1: Isometric (Cubic) • 6 sides • All sides are square • Examples *pyrite *halite *diamond *galena

  20. Type 2: Tetragonal • 6 sides • 4 rectangles, 2 squares (right angles) • Example *zircon

  21. Type 3: Hexagonal • 8 sides • 2 hexagons, 6 rectangles (right angles) • Examples *ice *quartz *emeralds

  22. Type 4: Orthorhombic • 6 sides • 6 rectangles (3 pairs of rectangles with different sizes at right angles) • Examples *topaz *barite

  23. Type 5: Monoclinic • 6 sides • 4 rectangles, 2 parallelograms (several angles) • Examples *gypsum *muscovite

  24. Type 6: Triclinic • 6 sides • Parallelograms (no right angles) • Example *turquoise

  25. Mineral with a Cubic or Isometric Crystal Shape • Pyrite has a Cubic Crystal Structure

  26. Mineral with a Tetragonal Crystal Shape • Rutile has a Tetragonal Crystal Structure

  27. Mineral with a Hexagonal Crystal Shape • Ruby has a Hexagonal Crystal Structure

  28. Minerals with Orthorhombic Crystal Shapes • The is a very big crystal system containing gemstones such as topaz, peridot, tanzanite, and many others

  29. Mineral with a Monoclinic Crystal Shape • Gypsum is a mineral with a Monoclinic Crystal Structure

  30. Mineral with a Triclinic Crystal Shape • Calcite- Triclinic crystal look like a rectangular box that someone pushed from one side to make it lean

  31. Hardness • One of the more useful properties for identification • Done by rubbing two minerals together, one will scratch the other unless they have the same hardness • Mohs Hardness Scale- 1-10 • Talc is the softest, what is hardest?

  32. Moh’s Hardness Scale

  33. Cleavage and Fracture • Cleavage is the tendency of a mineral to cleave or break along flat, even surfaces • Fracture is what happens to all other minerals that do not display cleavage • Fracture can be described as the uneven breakage of a mineral • Internal atomic structure determines whether a mineral will display cleavage or fracture

  34. Fracture or Cleavage? Selena

  35. Density • Ratio of an objects mass to its volume • D= M/V • For minerals we would use g/cm3, since we are looking at solids • Density of pure minerals are of constant value. Therefore we can use density to identify pure minerals or to tell if a mineral is not in pure form.

  36. Other Properties • Magnetism- some types of magnetite are magnetic and can be used to pick of metal objects • Double Refraction- When calcite is placed over printed words the letters appear doubled • Chemical Reactions with HCl- Carbonate minerals will fizz when they come into contact with hydrochloric acid

  37. Double Refraction of Calcite

  38. Magnetism