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| an element is a substance composed entirely of chemically identical atoms |
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the smallest unit of a chemical element that can retain the properties of that element
an atom consists of energy in the form of an electron cloud around a central nucleus |
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| a link between neighboring atoms caused by the interaction of electrons |
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| a single substance produced by the chemical bonding of two or more different chemical elements |
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| a means of expressing the composition of a substance in terms of the proportions of its componenet chemical elements |
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| chemical elements within a material that are capable of causing selective absorption of visible light |
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silicate gem materials have structures built with bonded units of silicon and oxygen atoms
Ex) Quartz - SiO2 |
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certain chemical composed composed of one or more chemical elements combine from oxygen
Ex) Corundum - Al2O3 |
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compounds of carbon and oxygen bonded with metallic elements
Ex) Calcite - CaCO3 |
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compounds with phosphorous and oxygen
Ex) turquoise |
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| materials with at least some chemical componenets formed by a living organism |
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| natural, inorganic, crystalline materials which are formed by geological processes |
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| minerals and other materials are said to be non-crystalline, or amorphous, when they lack an overall orderly internal crystal structure |
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| a naturally-formed aggregate of minerals from the Earth's crust |
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| a word used to describe a single crystalline material with plane crystal faces; any material with single, continuous internal crystal structure including artifical single-face crystal materials |
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| individual crystals can be seen only under magnification |
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| substances which consist of many aggregated crystals; polycrystalline materials possess no overall exterial crystal form |
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| a substance consisting of masses of minute crystals, too small to be seen under an ordinary optical microscope |
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a plane surface of a crystal structure where unrestricted crystal growth has ceased
crystal faces tend to be parallel to those crystal structure layers that are most densely packed with atoms |
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| a set of crystal faces related by the symmetry of the crystal |
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| the overall, natural external shape taken by a crystal; it is the development of a crystal form, or the relative development of two or more different crystal forms |
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| an imaginary, regularly-repeating array of points or dots representing the repeat pattern of atoms, molecules, and bonding in a real crystal structure |
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| the regular, repeating, three-dimensional arrangement of bonded atoms |
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| an aid to description and classification which describes the repetition of the structure arrangement of atoms and bonds in a crystalline material |
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| simple classification of crystal structures based on essential crystal symmetry and crystallographic axes of reference |
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| describes those materials that possess crystal structure |
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| an imaginary line that represents a particular direction of repeat of atoms and bonds through a crystal structure and also the relative repeat distance along that direction |
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| a crystal with two or more parts in structural continuity but distinct from one another |
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the ability, possessed by some crystalline gem materials, to split along certain well-defined crystal structure planes to leave more or less flat cleavage faces
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| sets of fine lines or planes within or on the surface of crystals or fashioned materials |
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indentations on the surface of the face that follow the crystal structure
Ex) in beryl |
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raised areas of growth that follow the crystal surface
Ex) triangular growth marks on corundum |
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| Tetragonal Crystal System |
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| Orthorhombic Crystal System |
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| Monoclinic Crystal System |
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an amorphouse material is composed largely of randomly oriented atoms, molecules or minute crystalline sectors
the material therefore exhibits no overall crystal form or effects |
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a pattern of twinning in a crystal structure which can be seen as thin, parallel layers
parallel lamellar twinning striations may be visible inside or on the surface of a crystal such as chrysoberyl or corundum |
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a type of twinned crystal in which two individuals have so intergrown that they appear to have penetrated each other
sometimes the result is in the shape of a cross or star
seen in fluorite, spinel and diamond |
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v-shaped troughs or grooves in the surface of certain twinned crystals
these occur where crystal forms are developed on each part of a twinned crystal in such a way that an external angle of less than 180° exists between faces on each part of the twin |
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| an imaginary line which indicates a direction through a crystal structure about which the structure can be rotated to appear identical two, three, four or six times during one complete rotation |
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| an imaginary mirror plane dividing a crystal structure into two parts; either part can be reflected through the mirror and still appear identical to the other part |
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| three or four intersecting reference axes which represent the repeat directions and repeat distances in a single crystal structure |
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| materials in which the crystals grow outward in radiating masses to form a rounded or hummock-like appearance |
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| Stalagmitic and Stalactitic Habit |
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| cave and fissure deposits ranging from extended botryoidal to column-like, where successive layers have built into fluted, sheet-like deposits or long, hanging or protruding masses of mineral |
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| branching, fern-like or moss-like crystal growth which occurs as inclusions or within cracks in minerals |
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| a mineral which takes on the external shapes or crystal habit of a different mineral as a result of alteration or chemical replacement of the original mineral |
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| a chemical element or compound may have two or more alternative crystal structures |
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| materials that can contain alternative atoms within the same basic crystal structure |
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| the replacement of one chemical element by another in a crystalline material; the crystal structure remains teh same, but the physical properties vary |
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| a state in which a material has become almost amorphous (non-crystalline) due to the breakdown of the original crystal structure by radioactivity within the material |
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crystalline amterials exhibit directional properties; these properties are controlled by the crystal structure of the material
Ex) hardness, pleochroism and surface markins on cyrstals |
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