Lesson 5 Earth and Earth Resources - Mineral.pptx

Minerals

1. Minerals This Photo by Unknown author is licensed under CC BY-SA-NC .

2. Mineral

3. General Characteristics of Minerals

4. Examples of minerals halite (salt) for cooking graphite (pencil) for writing diamond and gold as jewelry

5. Crystal Structure of Minerals Crystal structure is dependent on the chemical composition of the mineral Minerals with the same chemical compositions often share the same crystal structure and belong to the same crystal system.

6. Physical Properties of Minerals

7. Crystal Form/Habit The external shape of a crystal or groups of crystals is displayed / observed as these crystals grow in open spaces.  The form reflects the supposedly internal structure (of atoms and ions) of the crystal (mineral).  It is the natural shape of the mineral before the development of any cleavage or fracture. The crystal form also defines the relative growth of the crystal in three dimensions (length,  width, and height)

8. Crystal Form or Habit

9. Cleavage It is the weak plane after the mineral is formed. It is the property of some minerals to break along parallel repetitive planes of weakness to form smooth, flat surfaces. These planes of weakness are inherent in the bonding of atoms that makes up the mineral. These planes of weakness are parallel to the atomic planes and appear to be repeating within the mineral. When minerals break evenly in more than one direction, cleavage is described by the number of cleavage directions and the angle(s) between planes (e.g. cleavage in 2 directions at 90 degrees to each other).

10. Some minerals may not have cleavages but exhibit broken surfaces that are irregular and non-planar.  Quartz for example has an inherent weakness in the crystal structure that is not planar.  Examples of fracture are conchoidal, fibrous, hackly, and uneven among others.

11. Luster it is the quality and intensity of reflected light exhibited by the mineral Metallic – generally opaque and exhibit a resplendent shine similar to a polished metal Non-metallic vitreous (glassy) adamantine (brilliant/diamond-like) resinous silky pearly dull (earthy) greasy

12. Hardness Measured using Mohs’ Scale by Friedrich Mohs (1812) The test compares the resistance of a mineral relative to the 10 reference minerals with known hardness. It is simply determining the hardness of a mineral by scratching them with common objects of known hardness (e.g. copper coin -3.0-3.5)

13. Pros and Cons of Mohs’ Scale PROs: Easy to do the test  Can be done anywhere, anytime as long as the place is not dark Mohs scale is highly relevant for field geologists to roughly identify minerals using scratch kits Can be done without or few kits – handy CONs: The scale is qualitative and not quantitative Cannot be used to test accurate hardness of industrial materials

14. Color and Streak Color maybe a unique identifying property of certain minerals (e.g. malachite – green, azurite – blue). There are also lots of minerals that share similar or the same color/s. In addition, some minerals can exhibit a range of colors. The mineral quartz for example, can be pink (rose quartz), purple (amethyst), orange (citrine), white (colorless quartz) etc. Streak is the color of a mineral in powdered form. Streak (red) Color (black) Color and streak of a hematite

15. Color and Streak The color of a mineral could be different from the streak.  Streak is a better diagnostic property compared with color.  Streak is inherent to almost every mineral. Color maybe unreliable for identification as impurities within the minerals may give the minerals a different color. Example: Pyrite (FeS2) exhibits a golden color (hence the other term for pyrite is Fool’s Gold) but has a black or dark gray streak.

16. Specific Gravity It is the ratio of the weight of a mineral to the weight of an equal volume of water. It is a measure to express the density (mass per unit volume) of a mineral. The specific gravity of a mineral is numerically equal to density. A bucket of silver (SG 10) would weigh 10 times more than a bucket of water (SG 1).

17. Tenacity – reaction to stress Brittleness – A mineral can be turned into powder Malleability – A mineral can be flattened by pounding Ductility – A mineral can be stretched into wire Flexibility – A mineral can be bent Elasticity – A mineral can bring back its original shape Sectility – A mineral can be sliced by a knife

18. Other Properties Others – There are certain unique properties of minerals that actually help in their identification (e.g. magnetism, odor, taste, tenacity, reaction to acid, etc.). Magnetite is strongly magnetic; sulfur has distinctive smell; halite is salty; calcite fizzes with acid as with dolomite but in powdered form.