WELCOME TO THE GLENDALE COMMUNITY COLLEGE MINERAL IDENTIFICATION PROGRAM

Transcription

1 presented by: WELCOME TO THE GLENDALE COMMUNITY COLLEGE MINERAL IDENTIFICATION PROGRAM Susan Celestian - Curator of the Arizona Mining and Mineral Museum Stan Celestian - Photographer copyright 2002

2 Where do minerals come from? Minerals from magma Magma rises from the mantle and cools When it cools, it crystallizes into minerals. If it cools quickly, it forms small crystals. (granite) If it cools slowly, it forms large crystals. (salt)

3 Where do minerals come from? Minerals from solutions Minerals can dissolve into a solution. When enough minerals are in the solution, they stick together and precipitate. They form a solid while still in the solution. Minerals can also crystallize when the solution evaporates (called evaporites)

4 What is a Mineral? Cubic Fluorite Crystal 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

5 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. Tourmaline Crystal from Brazil

6 What is a Mineral? Inorganic Barite Rose - A flower like growth of Barite crystals. Minerals are NOT produced by organic processes. NOT a Mineral List Teeth Bones sea shells kidney stones Pearls Coral Coal Amber

7 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 Halite (salt) from Searles Lake, CA Red = Sodium Green = Chlorine

8 What is a Mineral? Definite Chemical Composition Halite - NaCl For every atom of Sodium there is an atom of Chlorine. 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.

9 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

10 PHYSICAL PROPERTIES HARDNESS In this photo, a quartz crystal has been rubbed across a glass plate. The result is that the glass plate was scratched. The quartz is therefore harder than the glass. Quartz is harder than 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.

11 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.

12 PHYSICAL PROPERTIES HARDNESS MOH S SCALE OF MINERAL HARDNESS 1. TALC 6. FELDSPAR 2. GYPSUM 7. QUARTZ 3. CALCITE 8. TOPAZ 4. FLUORITE 9. CORUNDUM 5. APATITE 10. DIAMOND OTHER MATERIALS COMMONLY USED: FINGERNAIL 3 - COPPER PENNY GLASS STEEL FILE

13 PHYSICAL PROPERTIES CLEAVAGE CLEAVAGE is 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 90 o angles along the edges. These are FLUORITE cleavage fragments.

14 PHYSICAL PROPERTIES CLEAVAGE Within this crystalline pattern it is easy to see how atoms will separate to produce cleavage with cubic (90 o ) angles.

15 PHYSICAL PROPERTIES CLEAVAGE These pictures show different cleavage angles and the quality of cleavage. Fluorite has cleavage in four directions Mica A thin has sheet perfect of Muscovite cleavage in seen ONE on direction. edge.

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

17 PHYSICAL PROPERTIES CLEAVAGE Rhombohedral Cleavage - 3 directions CALCITE Even these tiny fragments have rhombohedral cleavage.

18 PHYSICAL PROPERTIES CLEAVAGE Blocky Cleavage 2 directions Orthoclase Feldspar Orthoclase feldspar has good Note that the faces in the circle are at cleavage in 2 directions. different levels. By adjusting the lighting, The all of blocky the parallel appearance faces will of this reflect specimen is a simultaneously. hint that it has cleavage. This results The in a clue flash that of the light specimen from all has the parallel cleavage faces. 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.

19 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.

20 PHYSICAL PROPERTIES CLEAVAGE FLUORITE cleavage octahedron

21 PHYSICAL PROPERTIES FRACTURE FRACTURE is 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.

22 PHYSICAL PROPERTIES FRACTURE This Quartz crystal has been struck with a hammer to show how the external form of the crystal does not repeat when broken. This is a good example of conchoidal fracture. Note the smooth curved surfaces.

23 PHYSICAL PROPERTIES STREAK STREAK is defined as the color of the mineral in powder form. Hematite on Streak Plate 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.

24 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. Sphalerite has a light yellow streak. 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.

25 PHYSICAL PROPERTIES LUSTER LUSTER is defined as the quality of reflected light. Minerals have been grossly separated into either METALLIC or NON- METALLIC lusters. Following are some examples: Native Silver has a Metallic Luster

26 PHYSICAL PROPERTIES LUSTER METALLIC Stibnite Galena Pyrite Marcasite

27 NON-METALLIC LUSTER VITREOUS Olivine - Peridot Quartz Wulfenite Spinel

28 NON METALLIC LUSTER Miscellaneous Lusters Asbestos - Silky Apophyllite - Pearly Graphite has a greasy or submetallic luster and easily marks paper. Sphalerite - Resinous Limonite - Dull or Earthy

29 PHYSICAL PROPERTIES 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. This is the same piece but the left side has been buffed with a steel brush. Note the bright metallic luster.

30 PHYSICAL PROPERTIES COLOR The COLOR of 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.

31 PHYSICAL PROPERTIES COLOR Amethyst Ionic Iron Clear - Without Impurities Hematite Inclusions Chlorite inclusions Various colors of Quartz.

32 INDICATIVE COLOR Azurite Sulfur Rhodochrosite Turquoise Malachite

33 PHYSICAL PROPERTIES MAGNETISM MAGNETISM is 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 strongly magnetic in that a magnet will easily be attracted to it.

34 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.

35 PHYSICAL PROPERTIES MAGNETISM This is a sample of black sand from Lynx Creek, Arizona. Its dark color is due to its high concentration of magnetite. See what happens when a magnet is place beneath the bottom right portion of the paper. This technique is used to separate out much of the unwanted material in the search for gold in placer deposits.

36 PHYSICAL PROPERTIES MAGNETISM LODESTONE is a variety of Magnetite that is naturally a magnet.

37 PHYSICAL PROPERTIES DIAPHANEITY The manner in which minerals transmit light is called DIAPHANEITY and is expressed by these terms: TRANSPARENT: A mineral is considered to be transparent if the outline of an object viewed through it is distinct. TRANSLUCENT: A mineral is considered to be translucent if it transmits light but no objects can be seen through it. OPAQUE: A mineral is considered to be opaque if, even on its thinnest edges, no light is transmitted. Quartz with Spessartine Garnets

38 PHYSICAL PROPERTIES DIAPHANEITY TRANSPARENT: A mineral is considered to be transparent if the outline of an object viewed through it is distinct. Topaz from Topaz Mountain, Utah

39 PHYSICAL PROPERTIES DIAPHANEITY TRANSLUCENT: A mineral is considered to be translucent if it transmits light but no objects can be seen through it. Sylvite from Salton Sea, California Backlit Apophyllite Crystals

40 PHYSICAL PROPERTIES DIAPHANEITY OPAQUE: A mineral is considered to be opaque if, even on its thinnest edges, no light is transmitted. Schorl - The black variety of Tourmaline

41 DOUBLE REFRACTION DOUBLE REFRACTION: Is a property shared by many minerals ( but not those in the isometric crystal system). It is best displayed in the mineral CALCITE. This image clearly shows the double image below the calcite

42 CHEMICAL PROPERTIES REACTION TO HYDROCHLORIC ACID Some minerals, notably the carbonates, react to cold dilute HCl. In this illustration a piece of CALCITE is shown to react (fizz) after HCl is applied. Calcite Reacts to HCl

43 Uses of Rocks and Minerals

44 Mineral Identification RESOURCES For lots of useful images of minerals and more facts about minerals, check out this web site:

45 This copyrighted Power Point CD was produced strictly for educational purposes. Any attempt at using the images within this program for monetary gain is illegal. The authors have given permission to use the program or parts of it, provided THE credit is given to the Arizona Mining and Mineral Museum, its Curator -END Susan Celestian and the photographer - Stan Celestian.