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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

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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 (*)

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

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

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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 TRICLINIC (*) Drusy Quartz on Barite

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Mineral Identification Basics PHYSICAL PROPERTIES CRYSTALS ISOMETRIC - Fluorite Crystals The first group is the ISOMETRIC. This literally means “equal measure” and refers to the equal size of the crystal axes. (*)

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Mineral Identification Basics ISOMETRIC CRYSTALS ISOMETRIC In this crystal system there are 3 axes. Each has the same length as indicated by the same letter “a”. They all meet at mutual 90 o angles in the center of the crystal. Crystals in this system are typically blocky or ball-like. (*) ISOMETRIC Basic Cube a3 a2 a1

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Mineral Identification Basics ISOMETRIC CRYSTALS ISOMETRIC Crystal Model (*) Within this ISOMETRIC crystal model is the OCTAHEDRAL crystal form (yellow) and the TETRAHEDRAL crystal form (shown by the black lines). (*)

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Mineral Identification Basics ISOMETRIC CRYSTALS ISOMETRIC - Basic Cube (*) a1 a3 a2 a3 a2 a1 Fluorite cube with crystal axes. (*)

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Mineral Identification Basics ISOMETRIC BASIC CRYSTAL SHAPES Octahedron Spinel Cube Fluorite Pyrite Cube with Pyritohedron Striations Trapezohedron Garnet Garnet - Dodecahedron These are all examples of ISOMETRIC Minerals. (*)

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Mineral Identification Basics HEXAGONAL CRYSTALS HEXAGONAL - Three horizontal axes meeting at angles of 120 o and one perpendicular axis. (*) a1 a2 a3 HEXAGONAL Crystal Axes c

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Mineral Identification Basics HEXAGONAL CRYSTALS HEXAGONAL Crystal Model (*) 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.(*)

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Mineral Identification Basics HEXAGONAL CRYSTALS These hexagonal CALCITE crystals nicely show the six sided prisms as well as the basal pinacoid. (*) (*)

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Mineral Identification Basics HEXAGONAL CRYSTALS RHOMBOHEDRON Dolomite SCALENOHEDRON Rhodochrosite Quartz Hanksite Pyramid Face Prism Faces Pyramid Faces Vanadinite (*)

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Mineral Identification Basics TETRAGONAL CRYSTALS TETRAGONAL Two equal, horizontal, mutually perpendicular axes (a1, a2) (*) TETRAGONAL Crystal Axes a1 a2 c c a1 This is an Alternative Crystal Axes (*) Vertical axis (c) is perpendicular to the horizontal axes and is of a different length. (*)

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Mineral Identification Basics TETRAGONAL CRYSTALS TETRAGONAL Crystal Model (*) TETRAGONAL This model shows a tetragonal PRISM enclosing a DIPYRAMID. (*)

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Mineral Identification Basics TETRAGONAL CRYSTALS WULFENITE Same crystal seen edge on. Same crystal seen edge on. (*)

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Mineral Identification Basics TETRAGONAL CRYSTALS APOPHYLLITE (clear) on Stilbite (*) This is the same Apophyllite crystal looking down the “c” axis. The red square shows the position of the pinacoid (perpendicular to the “c” axis). (*) C axis line

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Mineral Identification Basics ORTHORHOMBIC CRYSTALS ORTHORHOMBIC Three mutually perpendicular axes of different lengths. (*) ORTHORHMOBIC Crystal Axes a b c a c b An Alternative Crystal Axes Orientation (*)

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Mineral Identification Basics ORTHORHOMBIC CRYSTALS ORTHORHMOBIC Crystal Model (*) 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. (*)

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Mineral Identification Basics ORTHORHOMBIC CRYSTALS Topaz from Topaz Mountain, Utah. (*)

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Mineral Identification Basics ORTHORHOMBIC CRYSTALS The view above is looking down the “c” axis of the crystal. (*) C axis B axis A axis BARITE is also orthorhombic. (*) C axis A axis B axis (*)

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Mineral Identification Basics ORTHORHOMBIC CRYSTALS STAUROLITE (*) Prism View (*) Pinacoid View (*) This is a Staurolite TWIN with garnets attached. (*)

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Mineral Identification Basics MONOCLINIC CRYSTALS MONOCLINIC In this crystal form the axes are of unequal length. (*) MONOCLINIC Crystal Axes a b c But a and c make some oblique angle and with each other. (*) Axes a and b are perpendicular. (*) Axes b and c are perpendicular. (*)

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Mineral Identification Basics MONOCLINIC CRYSTALS MONOCLINIC Crystal Model MONOCLINIC In this model the outside shape is the PRISM. It looks like a distorted brick - flattened out of shape. Inside is the DIPYRAMID. (*)

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Mineral Identification Basics MONOCLINIC CRYSTALS Gypsum Mica Orthoclase Top View (*)

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Mineral Identification Basics TRICLINIC CRYSTALS TRICLINIC In this system, all of the axes are of different lengths and none are perpendicular to any of the others. (*) TRICLINIC Crystal Axes a b c

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Mineral Identification Basics TRICLINIC CRYSTALS TRICLINIC Crystal Model (*) TRICLINIC Again in this model the outside shape is the PRISM. Located within the prism is the DIPYRAMID. (*)

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Mineral Identification Basics TRICLINIC CRYSTALS Microcline, variety Amazonite (*)

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Mineral Identification RESOURCES For lots of useful images of minerals and more facts about minerals, check out this web site: F or 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: To contact the Arizona Department of Mines and Mineral Resources, the web site address is:

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