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## Mineral Identification Basics

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**Mineral Identification Basics**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**Mineral Identification Basics**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 (*)**Mineral Identification Basics**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 (*)**Mineral Identification Basics**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 (*)**Mineral Identification Basics**PHYSICAL PROPERTIES CRYSTALS A CRYSTAL is the outward form of the internal structure of the mineral. The 6 basic crystal systems are: (*) ISOMETRIC HEXAGONAL TETRAGONAL ORTHORHOMBIC MONOCLINIC Drusy Quartz on Barite TRICLINIC (*)**Mineral Identification Basics**PHYSICAL PROPERTIES CRYSTALS The first group is the ISOMETRIC. This literally means “equal measure” and refers to the equal size of the crystal axes. (*) ISOMETRIC - Fluorite Crystals**Mineral Identification Basics**ISOMETRIC CRYSTALS a3 a2 a1 ISOMETRIC Basic Cube ISOMETRIC In thiscrystal system there are 3 axes. Each has the same length as indicated by the same letter “a”. They all meet at mutual 90o angles in the center of the crystal. Crystals in this system are typically blocky or ball-like. (*)**Mineral Identification Basics**ISOMETRIC CRYSTALS Within this ISOMETRIC crystal model is the OCTAHEDRAL crystal form (yellow) and the TETRAHEDRAL crystal form (shown by the black lines). (*) ISOMETRIC Crystal Model (*)**Mineral Identification Basics**ISOMETRIC CRYSTALS a3 a1 a2 Fluorite cube with crystal axes. (*) a3 a2 a1 ISOMETRIC - Basic Cube (*)**Mineral Identification Basics**ISOMETRIC BASIC CRYSTAL SHAPES Pyrite Fluorite Cube Cube with Pyritohedron Striations Garnet Trapezohedron Spinel Octahedron These are all examples of ISOMETRIC Minerals. (*) Garnet - Dodecahedron**Mineral Identification Basics**HEXAGONAL CRYSTALS c a3 a2 a1 HEXAGONAL - Three horizontal axes meeting at angles of 120o and one perpendicular axis. (*) HEXAGONAL Crystal Axes**Mineral Identification Basics**HEXAGONAL CRYSTALS HEXAGONAL This model represents a hexagonal PRISM (the outside hexagon - six sided shape). The top and bottom faces are called PINACOIDS and are perpendicular to the vertical “c” axis. Within this model is the SCALENOHEDRAL form. Each face is a scalenohedron. Calcite often crystallizes with this form. As the model rotates, the flash of light seen is from a scalenohedral face.(*) HEXAGONAL Crystal Model (*)**Mineral Identification Basics**HEXAGONAL CRYSTALS These hexagonal CALCITE crystals nicely show the six sided prisms as well as the basal pinacoid. (*) (*)**Mineral Identification Basics**HEXAGONAL CRYSTALS Pyramid Face Prism Faces Rhodochrosite Dolomite SCALENOHEDRON RHOMBOHEDRON Quartz Pyramid Faces Prism Faces Vanadinite (*) Hanksite**Mineral Identification Basics**TETRAGONAL CRYSTALS c a2 a1 c a2 TETRAGONAL Crystal Axes a1 This is an Alternative Crystal Axes (*) TETRAGONAL Two equal, horizontal, mutually perpendicular axes (a1, a2) (*) Vertical axis (c) is perpendicular to the horizontal axes and is of a different length. (*)**Mineral Identification Basics**TETRAGONAL CRYSTALS TETRAGONAL This model shows a tetragonal PRISM enclosing a DIPYRAMID. (*) TETRAGONAL Crystal Model (*)**Mineral Identification Basics**TETRAGONAL CRYSTALS Same crystal seen edge on. (*) WULFENITE**Mineral Identification Basics**TETRAGONAL CRYSTALS C axis line This is the same Apophyllite crystal looking down the “c” axis. APOPHYLLITE (clear) on Stilbite (*) The red square shows the position of the pinacoid (perpendicular to the “c” axis). (*)**Mineral Identification Basics**ORTHORHOMBIC CRYSTALS c c b b a a ORTHORHOMBIC Three mutually perpendicular axes of different lengths. (*) An Alternative Crystal Axes Orientation (*) ORTHORHMOBIC Crystal Axes**Mineral Identification Basics**ORTHORHOMBIC CRYSTALS ORTHORHOMBIC This model shows the alternative axes where the vertical “c” axis is not the longest axis. (*) The model shows the outside “brick” shape of the PRISM and the inner shape is a DIPYRAMID. The top and bottom faces are called PINACOIDS and are perpendicular to the “c” axis. (*) ORTHORHMOBIC Crystal Model (*)**Mineral Identification Basics**ORTHORHOMBIC CRYSTALS Topaz from Topaz Mountain, Utah. (*)**Mineral Identification Basics**ORTHORHOMBIC CRYSTALS C axis C axis B axis B axis A axis A axis The view above is looking down the “c” axis of the crystal. (*) (*) BARITE is also orthorhombic. (*)**Mineral Identification Basics**ORTHORHOMBIC CRYSTALS Pinacoid View (*) Prism View (*) STAUROLITE (*) This is a Staurolite TWIN with garnets attached. (*)**Mineral Identification Basics**MONOCLINIC CRYSTALS c b a MONOCLINIC Crystal Axes MONOCLINIC In this crystal form the axes are of unequal length. (*) Axes a and b are perpendicular. (*) Axes b and c are perpendicular. (*) But a and c make some oblique angle and with each other. (*)**Mineral Identification Basics**MONOCLINIC CRYSTALS MONOCLINIC In this model the outside shape is the PRISM. It looks like a distorted brick - flattened out of shape. Inside is the DIPYRAMID. (*) MONOCLINIC Crystal Model**Mineral Identification Basics**MONOCLINIC CRYSTALS Top View (*) Gypsum Orthoclase Mica**Mineral Identification Basics**TRICLINIC CRYSTALS c b a TRICLINIC Crystal Axes TRICLINIC In this system, all of the axes are of different lengths and none are perpendicular to any of the others. (*)**Mineral Identification Basics**TRICLINIC CRYSTALS TRICLINIC Again in this model the outside shape is the PRISM. Located within the prism is the DIPYRAMID. (*) TRICLINIC Crystal Model (*)**Mineral Identification Basics**TRICLINIC CRYSTALS Microcline, variety Amazonite (*)**Mineral IdentificationRESOURCES**For lots of useful images of minerals and more facts about minerals, check out this web site: http://www.gc.maricopa.edu/earthsci/imagearchive/index.htm For lots of up-to-date information about the Museum’s activities, be sure and visit the Arizona Mining and Mineral Museum’s web site at: http://www.admmr.state.az.us/musgen.htm To contact the Arizona Department of Mines and Mineral Resources, the web site address is: http://www.admmr.state.az.us/