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PHYSICAL SCIENCE 120 PHYSICAL PROPERTIES OF MINERALS

PHYSICAL SCIENCE 120 PHYSICAL PROPERTIES OF MINERALS. As you view the PHS 120 Power Points you will be prompted to advance to the next slide when you see this symbol (*). (*). TABLE OF CONTENTS. Physical Science 120 students are required to do pages 1 – 54. Mineral Definition……………….……Slide 3

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PHYSICAL SCIENCE 120 PHYSICAL PROPERTIES OF MINERALS

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  1. PHYSICAL SCIENCE 120PHYSICAL PROPERTIES OF MINERALS As you view the PHS 120 Power Points you will be prompted to advance to the next slide when you see this symbol (*). (*)

  2. TABLE OF CONTENTS Physical Science 120 students are required to do pages 1 – 54. Mineral Definition……………….……Slide 3 Hardness……………………………………..8 Cleavage……………………………….…...12 Fracture……………………………..…..….19 Streak………………………………………21 Luster…………………………..……….….23 Color……………………………………….28 Specific Gravity…………………………....31 Taste……………………………………….48 Magnetism…………………………………49 Double Refraction…………………………53 Reaction to HCl (acid)…………………….54 Diaphaneity………………………………..56 Crystals………………………………….…60 Isometric……………………………….…..62 Hexagonal……………………………….…66 Tetragonal………………………………….70 Orthorhombic…………………………..…..74 Monoclinic………………………………....79 Triclinic…………………………………….82 Resources…………………………………..85 This list of slides will allow you to review the various topics of the presentation. (*) During the presentation you can “right mouse click” on a slide to go to the edit mode. (*)

  3. Mineral Identification Basics What is a Mineral? There is a classic four part definition for mineral. Minerals must be: (*) • Naturally occurring (*) • Inorganic (*) • Possess a definite crystalline structure (*) • Have a definite chemical composition (*) Cubic Fluorite Crystal

  4. Mineral Identification Basics What is a Mineral? Naturally Occurring (*) • Minerals are not synthetic - they are produced by the natural geological processes working on Earth. For example, steel, brass, bronze and aluminum are not considered minerals in that they are not found in nature. (*) • Technically speaking, synthetic gemstones are not considered minerals. This area of mineralogy has a hazy boundary in that synthetic stones are in every way the same as the natural stones. But because they are produced in laboratories, they do not meet the classic definition of a mineral. (*) • Also note that many synthetic gemstones are “doped” with a fluorescent dye to distinguish them from natural stone. (*) Tourmaline Crystal from Brazil

  5. Mineral Identification Basics What is a Mineral? Inorganic (*) • Minerals are NOT produced by organic processes. As a result things like pearls, coral, coal and amber are not considered minerals. • Also included in this • “NOTa Mineral List” are teeth, bones, sea shells and even kidney stones. (*) Barite Rose - A flower like growth of Barite crystals.

  6. Mineral Identification Basics What is a Mineral? Internal Structure Minerals are the result of atoms joining together through electrical bonds to produce a definite internal structure. (*) It is the nature of the atoms and the strength of the chemical bonds that determine many of the minerals’ physical and chemical properties. (*) Crystalline Pattern of Halite Red = Sodium Green = Chlorine Halite (salt) from Searles Lake, CA (*)

  7. Mineral Identification Basics What is a Mineral? Definite Chemical Composition (*) • Minerals can be expressed by a chemical formula. The internal order of minerals means that there is a definite relationship in the number of atoms that makes up the mineral. (*) Halite - NaCl For every atom of Sodium there is an atom of Chlorine.

  8. Mineral Identification Basics PHYSICAL PROPERTIES HARDNESS HARDNESS is defined as the resistance a mineral has to being scratched - its “scratchability”. Hardness tests are done by scratching one mineral against another. The mineral that is scratched is softer than the other. (*) Pyrite Crystals Hardness of 6.5 (*)

  9. Mineral Identification Basics PHYSICAL PROPERTIES HARDNESS In this photo, a quartz crystal will be rubbed across a glass plate. The result is that the glass plate will be scratched. The quartz is therefore harder than the glass. (*) HINT: In doing a hardness test try to pick a smooth or flat surface on the mineral to be scratched. Try to pick a point or a sharp edge on the mineral that you think will do the scratching. Glass is usually a good place to start because it is in the middle of the hardness table, it has a flat, smooth surface and it is easily obtained. (*) Quartz is harder than glass.

  10. Mineral Identification Basics PHYSICAL PROPERTIES HARDNESS Care must be taken on some minerals that crumble easily. Remember that hardness is the resistance a mineral has to being scratched - NOT how easily it breaks apart. The physical property related to the ease in which a mineral breaks is tenacity. (*) Also be sure to determine the hardness of a mineral on a fresh surface whenever possible. Some minerals have a tendency to oxidize or corrode. These surface deposits usually have a different hardness than the fresh mineral. (*)

  11. Mineral Identification Basics PHYSICAL PROPERTIES HARDNESS MOH’S SCALE OF MINERAL HARDNESS 1. TALC 2. GYPSUM 3. CALCITE 4. FLUORITE 5. APATITE (*) 6. FELDSPAR 7. QUARTZ 8. TOPAZ 9. CORUNDUM 10. DIAMOND (*) OTHER MATERIALS COMMONLY USED: 2.5 - FINGERNAIL 3 - COPPER PENNY 5.5 - GLASS 6-6.5 - STEEL FILE Moh’s scale is a list of minerals with increasing hardness.(*) (*)

  12. Mineral Identification Basics PHYSICAL PROPERTIES CLEAVAGE These are FLUORITE cleavage fragments. (*) CLEAVAGEis the property of a mineral that allows it to break repeatedly along smooth, flat surfaces. (*) These GALENA cleavage fragments were produced when the crystal was hit with a hammer. Note the consistency of the 90o angles along the edges. (*)

  13. Mineral Identification Basics PHYSICAL PROPERTIES CLEAVAGE Within this crystalline pattern it is easy to see how atoms will separate to produce cleavage with cubic (90o) angles. (*) It is similar to tearing a piece of paper that has perforations in it. The paper has a tendency to tear along the perforations. They are zones of weakness. (*) In this example the lines represent breaks between the atoms that make up the mineral. Cleavage is guided by the atomic structure. (*)

  14. Mineral Identification Basics PHYSICAL PROPERTIES CLEAVAGE Fluorite has cleavage in four directions. (*) Mica has perfect cleavage in ONE direction. (*) A thin sheet of Muscovite seen on edge. These pictures show different cleavage angles and the quality of cleavage.

  15. Mineral Identification Basics PHYSICAL PROPERTIES CLEAVAGE These 3 directions of cleavage are mutually perpendicular resulting in cubic cleavage. (*) Common salt (the mineral HALITE) has very good cleavage in 3 directions. (*)

  16. Mineral Identification Basics PHYSICAL PROPERTIES CLEAVAGE Rhombohedral Cleavage - 3 directions CALCITE (*) Even these tiny fragments have rhombohedral cleavage. (*)

  17. Mineral Identification Basics PHYSICAL PROPERTIES CLEAVAGE Blocky Cleavage 2 directions Note that the faces in the circle are at different levels. By adjusting the lighting, all of the parallel faces will reflect simultaneously. This results in a flash of light from all the parallel faces. (*) Orthoclase feldspar has good cleavage in 2 directions. The blocky appearance of this specimen is a hint that it has cleavage. The clue that the specimen has cleavage is the fact that numerous faces will reflect light at the same time. Each face is parallel and light will reflect of each face producing a flash of light. (*) Orthoclase Feldspar (*)

  18. Mineral Identification Basics PHYSICAL PROPERTIES CLEAVAGE TALC has micaceous cleavage. That is to say that it cleaves like mica (1 perfect direction) but, in talc the crystals are so small that they cannot easily be seen. Instead the effect is that the talc “feels soapy”. The second picture shows some of the talc that has cleaved onto the fingers. (*) (*)

  19. Mineral Identification Basics PHYSICAL PROPERTIES FRACTURE FRACTUREis defined as the way a mineral breaks other than cleavage. (*) This is a piece of volcanic glass called OBSIDIAN. Even though it is NOT a mineral, it is shown here because it has excellent conchoidal fracture. (*) If you try this yourself, use caution. Conchoidal fracture in obsidian can produce extremely sharp edges. (*)

  20. Mineral Identification Basics PHYSICAL PROPERTIES FRACTURE This Quartz crystal will be struck with a hammer to show how that the external form of the crystal does not repeat when broken. (The flat crystal faces are not cleavage faces.) This is a good example of conchoidal fracture. (*) Note the smooth curved surfaces. (*)

  21. Mineral Identification Basics PHYSICAL PROPERTIES STREAK Hematite on Streak Plate STREAKis defined as the color of the mineral in powder form. (*) Streak is normally obtained by rubbing a mineral across a “streak plate”. This is a piece of unglazed porcelain. The streak plate has a hardness of around 7 and rough texture that allows the minerals to be abraded to a powder. This powder is the streak. (*) Hematite has a reddish brown streak. (*)

  22. Mineral Identification Basics PHYSICAL PROPERTIES STREAK Sphalerite is a dark mineral, however, it has a light colored streak. Next to the reddish brown streak of hematite is a light yellow streak. This is the streak of the sphalerite. (*) Light colored streaks are often difficult to see against the white streak plate. It is often useful to rub your finger across the powder to see the streak color. (*) Sphalerite has a light yellow streak. (*)

  23. Mineral Identification Basics PHYSICAL PROPERTIES LUSTER LUSTERis defined as the quality of reflected light. Minerals have been grossly separated into either METALLIC or NON-METALLIC lusters. Following are someexamples: (*) Native Silver has a Metallic Luster. (*)

  24. Mineral Identification Basics PHYSICAL PROPERTIES LUSTER METALLIC Stibnite Galena Pyrite (*) Marcasite The basic idea for Metallic Luster is that the minerals look like metals. (*)

  25. Mineral Identification Basics NON-METALLICLUSTER VITREOUS Olivine - Peridot Wulfenite Quartz (*) Spinel Vitreous Luster means that the mineral has a “glassy” look. Normally we think of glass as being clear, but there are many different colors of glass and they are all very “glassy” looking. Even china plates and glazed porcelain are vitreous. Here are some examples: (*)

  26. Mineral Identification Basics NON METALLICLUSTER Asbestos - Silky Apophyllite – Pearly (*) Graphite has a greasy or submetallic luster and easily marks paper. (*) Sphalerite - Resinous Limonite - Dull or Earthy Miscellaneous Lusters

  27. Mineral Identification Basics PHYSICAL PROPERTIES LUSTER This is the same piece but the left side has been buffed with a steel brush. Note the bright metallic luster. (*) The moral to this story is to look at a fresh surface whenever possible.(*) This piece of Native Copper is severely weathered. It does not look metallic. (*)

  28. Mineral Identification Basics PHYSICAL PROPERTIES COLOR The COLORof a mineral is usually the first thing that a person notices when observing a mineral. However, it is normally NOT the best physical property to begin the mineral identification process. (*) Following are some examples of color variation within mineral species followed by minerals that have a distinctive color: (*) Various colors of CALCITE. (*)

  29. Mineral Identification Basics PHYSICAL PROPERTIES COLOR Amethyst Ionic Iron Hematite Inclusions Chlorite inclusions Clear - Without Impurities Quartz comes in a wide range of colors. It is very easily colored by even trace amounts of impurities. (*) Various colors of Quartz.

  30. Mineral Identification Basics INDICATIVE COLOR Azurite (*) Sulfur Malachite Turquoise Rhodochrosite Some minerals do have a certain color associated with them. Here are some examples: (*)

  31. Mineral Identification Basics PHYSICAL PROPERTIES SPECIFIC GRAVITY The SPECIFIC GRAVITY of a mineral is a measure of the mineral’s density. It is related to the types of elements that make up the mineral and how they are packed into the mineral’s atomic structure. (*) Gold has a Specific Gravity of 19.2. It is 19.2 times the weight of an equal volume of water. Water has a Specific Gravity of 1. (*) Gold in Quartz

  32. Mineral Identification Basics PHYSICAL PROPERTIES SPECIFIC GRAVITY The SPECIFIC GRAVITY of a mineral is determined by weighing the specimen in air and then weighing it in water. Here is the formula: (*) Weight in air Specific Gravity = (Weight in air) - (Weight in water ) (divided by) (*)

  33. Mineral Identification Basics PHYSICAL PROPERTIES SPECIFIC GRAVITY Triple Beam Balance This is the equipment used in the lab at GCC to determine Specific Gravity. (*)

  34. Mineral Identification Basics PHYSICAL PROPERTIES SPECIFIC GRAVITY The first thing to check in using the balance is to make sure it balances at the zero mark when the tray is empty. (*) This circle shows the zero mark and that the balance is calibrated correctly. (*)

  35. Mineral Identification Basics PHYSICAL PROPERTIES SPECIFIC GRAVITY Notches (*) NO Notches (*) Notice that the top three bars of the balance have notches. These are the positions in which the weights are REQUIRED to rest. (*) Balance is in “Balance” (*)

  36. Mineral Identification Basics PHYSICAL PROPERTIES SPECIFIC GRAVITY NO Notches (*) The bottom bar has no notch. Instead the weight (the small chrome sleeve sitting over the zero mark on the left) simply slides along this bar. It reads 0.1 to 0.01 grams. (*)

  37. Mineral Identification Basics PHYSICAL PROPERTIES SPECIFIC GRAVITY Selecting the right material. (*) Opal in Rhyolite Not just any mineral will do. In determining the specific gravity of a mineral it must be pure, free of pockets or cracks (places that can trap air) and it should not easily dissolve in water. (*) Calcite with Garnet Sphalerite Limonite Halite

  38. Mineral Identification Basics PHYSICAL PROPERTIES SPECIFIC GRAVITY The Limonite is full of pore spaces. It is almost like a sponge. When it is weighed in water it has numerous trapped air pockets that will make it lighter that it should be. (*) Opal in Rhyolite Calcite with Garnet Sphalerite Limonite Halite It would be difficult to get an accurate weight. (*)

  39. Mineral Identification Basics PHYSICAL PROPERTIES SPECIFIC GRAVITY This is not a pure specimen. It is a combination of two minerals. The result of the specific gravity process would only give you an average of the two minerals. (*) Opal in Rhyolite Calcite with Garnet Sphalerite Limonite Halite

  40. Mineral Identification Basics PHYSICAL PROPERTIES SPECIFIC GRAVITY The opal in rhyolite has the same problem as the calcite with garnet. It is not a pure sample (*) Opal in Rhyolite Calcite with Garnet Sphalerite Limonite Halite

  41. Mineral Identification Basics PHYSICAL PROPERTIES SPECIFIC GRAVITY Halite is a salt. When weighed in water it dissolves. It would be difficult to get an accurate reading as it would become lighter and lighter as it slowly dissolved. (*) Opal in Rhyolite Calcite with Garnet Sphalerite Limonite Halite

  42. Mineral Identification Basics PHYSICAL PROPERTIES SPECIFIC GRAVITY Sphalerite (pronounced: sfal er ite) is a good choice. It is a pure sample with no crack or pore spaces. And, it does not dissolve in water. (*) Opal in Rhyolite Calcite with Garnet Sphalerite Sphalerite Limonite Halite

  43. Mineral Identification Basics PHYSICAL PROPERTIES SPECIFIC GRAVITY 100 grams is too much. Weight in air = 37.0 grams (*) Determine the weight of the Sphalerite (*)

  44. Mineral Identification Basics PHYSICAL PROPERTIES SPECIFIC GRAVITY Weight in Water The weights are in the same place but now that the sphalerite is submerged in water it is lighter, and the balance is again out of balance. (*)

  45. Mineral Identification Basics PHYSICAL PROPERTIES SPECIFIC GRAVITY Weight in Water It is important to note that the specimen being weighed is not resting on the bottom of the beaker or touching its sides. It is also completely submerged beneath the water. (*)

  46. Mineral Identification Basics PHYSICAL PROPERTIES SPECIFIC GRAVITY 0 grams 20 grams 7 grams 0.94 grams Weight in Water (*) The weight of the sphalerite in water is 27.94 grams. (*)

  47. Mineral Identification Basics PHYSICAL PROPERTIES SPECIFIC GRAVITY Weight in air Weight in air Specific Gravity = Specific Gravity = (Weight in air) - (Weight in water ) (Weight in air) - (Weight in water ) 37.00 grams 37.00 grams 27.94 grams Specific Gravity = 4.06 Note that there are no units. The grams cancel out. This is a ratio of how heavy the mineral is compared to an equal volume of water. The sphalerite is 4.06 times heavier than water. (*)

  48. Mineral Identification Basics PHYSICAL PROPERTIES TASTE IT IS NOT RECOMMENDED THAT A TASTE TEST BE PERFORMED ON MINERALS AS A STANDARD PROCESS. SOME MINERALS ARE TOXIC. However, the mineral HALITE is common salt and has a unique taste. (*) Halite cubes from Trona, CA (*)

  49. Mineral Identification Basics PHYSICAL PROPERTIES MAGNETISM MAGNETISMis the ability of a mineral to be attracted by a magnet. This most commonly is associated with minerals rich in iron, usually magnetite. (*) This is a piece of MAGNETITE with a magnet adhering to it. Magnetite is a mineral that is strongly magnetic in that a magnet will easily be attracted to it. (*)

  50. Mineral Identification Basics PHYSICAL PROPERTIES MAGNETISM More sensitivity is achieved if instead of a large sample, small pieces are used. In this way, even weakly magnetic minerals will be attracted to the magnet. (*)

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