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Warm-up

Warm-up. What is the difference between a mineral and a rock? What properties can we use to identify minerals?. Minerals The Building Blocks of Rocks. Minerals - The Building Blocks of Rocks . Recall from chemistry that elements and compounds are collectively known as “substances.”

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Warm-up

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  1. Warm-up • What is the difference between a mineral and a rock? • What properties can we use to identify minerals?

  2. Minerals The Building Blocks of Rocks

  3. Minerals - The Building Blocks of Rocks • Recall from chemistry that elements and compounds are collectively known as “substances.” • Elements bond together to form “compounds.” • Elements and compounds have a definite chemical formula. • ex.) Elements: Na is sodium and Cl is chlorine. • ex.) Compound: NaCl is sodium chloride, or common table salt. • In geology, we normally call rocky elements and compounds “minerals.” • Sodium chloride is called rock salt, or halite, when we’re discussing minerals.

  4. Figure 2.2

  5. Minerals - The Building Blocks of Rocks A mineral is a naturally occurring solid chemical substance that is formed through geological processes and that has a characteristic chemical composition, a highly ordered atomic structure, and specific physical properties. By comparison, a rock, which we will study later, is an mixture of minerals and/or mineraloids and does not have a specific chemical composition. Minerals range in composition from pure elements and simple salts to very complex silicates with thousands of known forms. The study of minerals is called mineralogy.

  6. Figure 2.3

  7. Minerals - The Building Blocks of Rocks Fluorite A mineral is naturally occurring, inorganic, solid in phase, possesses an orderly internal structure of atoms, and has a definite chemical composition. Mineraloids, on the other hand, lack an orderly internal structure. Lechatelierite

  8. Minerals - The Building Blocks of Rocks Physical properties of minerals Color The color of a mineral is one of its most obvious attributes, and is one of the properties that is always given in any description. Color results from a mineral’s chemical composition, impurities that may be present, and flaws or damage in the internal structure. Color in minerals is caused by the absorption, or lack of absorption, of various wavelengths of light.

  9. Minerals - The Building Blocks of Rocks Physical properties of minerals Streak When you rub a mineral on a flat surface, the color of the powder left behind on the streak plate is the mineral's streak. The streak and color of some minerals are the same. For others, the streak may be quite different from the color.

  10. Although the color of a mineral may not be very helpful in identification, the streak, which is the color of the powered mineral, can be very useful.

  11. Minerals - The Building Blocks of Rocks Physical properties of minerals Feel Some specimens of a particular mineral may have a rough feel since they are composed of tiny, protruding crystals, while other specimens of the same mineral have a smooth texture. Therefore, a rough feel is not necessarily an identification factor. A greasy and smooth feel, however, are inherent to all specimens of the same mineral. Fibrous minerals have a distinct, silky feel.

  12. Minerals - The Building Blocks of Rocks Physical properties of minerals Hardness Mineral hardness is based on the ability of one natural sample of matter to scratch another. Diamond is the hardest known naturally occurring substance, whereas talc is the least hard.

  13. Minerals - The Building Blocks of Rocks Physical properties of minerals Hardness The hardness of a material is measured against the Mohs scale by finding the hardest material that the given material can scratch, and/or the softest material that can scratch the given material. For example, if some material is scratched by apatite but not by fluorite, its hardness on the Mohs scale would fall between 4 and 5.

  14. Mohs Scale of Hardness Figure 2.13

  15. Minerals - The Building Blocks of Rocks Physical properties of minerals Cleavage In mineral terms, cleavage describes how a crystal breaks when subject to stress on a particular plane. If part of a crystal breaks due to stress and the broken piece retains a smooth plane or crystal shape, the mineral has cleavage. A mineral that never produces any crystallized fragments when broken off due to stress has no cleavage.

  16. Minerals - The Building Blocks of Rocks Physical properties of minerals Habit Mineral habit is the shape of how a mineral tends to form. Types of mineral habits include columnar, blocky, acicular (needle-like), granular, lamellar or foliated (sheets easily split apart), botryoidal (like a bunch of grapes), fibrous, radiating, or dendritic (like a fern).

  17. The mineral quartz often exhibits good crystal shape

  18. Pyrite (fool’s gold) has two common crystal forms Figure 2.11

  19. Figure 2.12A bladed habit

  20. prismatic habit Figure 2.12B

  21. banded habit Figure 2.12C

  22. botryoidal habit Figure 2.12D

  23. Minerals - The Building Blocks of Rocks Physical properties of minerals Luster The luster of a mineral is the way its surface reflects light. In simplest terms, minerals have a metallic or non-metallic luster. A metallic luster is a shiny, opaque appearance similar to a bright chrome bumper on an automobile. Other shiny, but somewhat translucent or transparent lusters (glassy, adamantine), along with dull, earthy, waxy, and resinous lusters, are grouped as non-metallic.

  24. The freshly broken sample of galena (right) displays a metallic luster, while the sample on the left is tarnished and has a submetallic luster.

  25. Minerals - The Building Blocks of Rocks Physical properties of minerals Fracture Fracture is a description of the way a mineral tends to break. It is different from cleavage and parting, which are generally clean flat breaks along specific directions. Different minerals will break in different ways and leave a surface that can be described in a recognizable way. Is the broken area smooth? Irregular? Jagged? Splintery? These are some of the ways of describing fracture. Although many minerals break in similar ways, some have a unique fracture and this can be diagnostic.

  26. Minerals - The Building Blocks of Rocks Physical properties of minerals Fracture The most common fracture type is conchoidal. This is a smoothly curved fracture that is familiar to people who have examined broken glass. Sometimes described as a clam-shell fracture.  Quartz has this fracture type and almost all specimens that have been broken, demonstrate this fracture type very well.

  27. Conchoidal Fracture Figure 2.16

  28. Minerals - The Building Blocks of Rocks Physical properties of minerals Fracture Uneven is a type that is basically self explanatory. It is a common type that is found in anhydrite.

  29. Minerals - The Building Blocks of Rocks Physical properties of minerals Fracture Jagged fractures have sharp points or edges that catch on a finger that's rubbed across the surface. Usually this indicates a metal such as copper , a metal alloy or some sulfides or oxides.

  30. Minerals - The Building Blocks of Rocks Physical properties of minerals Fracture Splintery is a fracture type that occurs in fibrous or finely acicular minerals and in minerals that have a relatively stronger structure in one direction than the other two.  Chrysotile serpentine is a typical mineral with splintery fracture, and kyanite  is an example of a non-fibrous mineral that has this fracture.

  31. Minerals - The Building Blocks of Rocks Physical properties of minerals Fracture Earthy is a fracture that produces a texture similar to broken children's clay. It is found in minerals that are generally massive and loosely consolidated such as limonite.

  32. Minerals - The Building Blocks of Rocks Physical properties of minerals Specific Gravity Specific Gravity is a measure of the density of a mineral. At times it is such a useful property that it is the only way to distinguish some minerals without laboratory or optical techniques.

  33. Minerals - The Building Blocks of Rocks Physical properties of minerals Specific Gravity Gold an easily be distinguished from "fool's gold" by specific gravity alone Specific gravity is a unit-less measure, because it is derived from the density of the mineral divided by the density of water and thus all units cancel. However, since water's density equals 1 gram per cubic centimeter (at specific conditions), then a mineral's specific gravity would also correspond to a mineral's density as expressed in grams per cubic centimeter.

  34. Minerals - The Building Blocks of Rocks Physical properties of minerals Taste Taste is not the first property someone would associate with minerals, yet taste is sometimes a very good characteristic and a key to identification in some cases. The most commonly "tasted" mineral is halite or rock salt, but there are several other minerals that have a distinctive taste. • NOTE: Consult your instructor or a professional before tasting a mineral – some are poisonous! Examples: Borax (sweet alkaline), halcanthite (sweet metallic & slightly poisonous), Epsomite (bitter), Glauberite (bitter salty), Halite (salty), Hanksite (salty), Melanterite (sweet, astringent and metallic), Sylvite (bitter), Ulexite (alkaline)

  35. Minerals - The Building Blocks of Rocks Physical properties of minerals Smell Several minerals give off a distinctive odor in certain conditions. Sulfur, in normal room conditions, gives off a mild odor resembling the smell of a lighting match. However if heated or struck, it gives off a powerful odor like rotten eggs. Arsenic gives off a very mild garlic smell in normal room conditions. However, if heated or struck, it gives off a powerful garlic odor. Although only few minerals have a characteristic odor, odor is very useful identification key.

  36. Minerals - The Building Blocks of Rocks Physical properties of minerals Tenacity – Brittleness If a mineral is hammered and the result is a powder or small crumbs, it is considered brittle. Brittle minerals leave a fine powder if scratched, which is the way to test a mineral to see if it is brittle. The majority of all minerals are brittle. Minerals that are not brittle may be referred to as non-brittle minerals.

  37. Minerals - The Building Blocks of Rocks Physical properties of minerals Tenacity – Sectility Sectile minerals can be separated with a knife into thin slices, much like wax.

  38. Minerals - The Building Blocks of Rocks Physical properties of minerals Tenacity – Malleability If a mineral can be flattened by pounding with a hammer, it is malleable. All true metals are malleable.

  39. Minerals - The Building Blocks of Rocks Physical properties of minerals Magnetism Several minerals react when placed within a magnetic field. Some minerals are strongly attracted to the magnet, others are weakly attracted, and one mineral is repelled. There are also several minerals that are attracted to magnetic fields only when heated. The presence of iron in a mineral is responsible for the magnetic properties of minerals in virtually all cases.

  40. Minerals - The Building Blocks of Rocks Physical properties of minerals Double Refraction Double refraction is a phenomenon exhibited on all non-opaque minerals except for amorphous ones and ones that crystallize in the isometric system. A light ray enters the crystal and splits up into two separate rays, making anything observed through the crystal appear as double.

  41. Minerals - The Building Blocks of Rocks Physical properties of minerals Double Refraction In some minerals, such as the Iceland Spar variety of Calcite, double refraction is strongly seen. The double refraction is different in every mineral, and thus can be used to identify gems. Double refraction is measured with a refractometer.

  42. Minerals - The Building Blocks of Rocks Physical properties of minerals Reaction to Hydrochloric Acid An important property in minerals is how they react to acids. All of the minerals that have some reaction to acids tend to be carbonates and a few other minerals that contain significant amounts of carbonate ions. Carbon dioxide gas is given off. The bubbles or effervescence is the reaction we are looking for and indicates the presence of carbonate ions.

  43. Minerals - The Building Blocks of Rocks Physical properties of minerals Reaction to hydrochloric acid With calcite and aragonite, the two most common carbonate minerals, the reaction to a cold, dilute acid is easily accomplished and is often so energetic that it is associated with a fizzing noise.

  44. The Rock-Forming Minerals The eight elements that compose most rock-forming minerals are oxygen (O), silicon (Si), aluminum (Al), iron (Fe), calcium (Ca), sodium (Na), potassium (K), and magnesium (Mg). The most abundant atoms in Earth’s crust are oxygen (46.6% by weight) and silicon (27.7% by weight) Composition of the Continental Crust

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