Amorphous
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Refers to any material which has no fixed, regular internal (atomic) structure.
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Cleavage
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The flat plane along which a crystal will easily break.
This is caused by weaknesses in the crystal's internal (atomic) structure.
Also see Fracture.
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Cryptocrystalline
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Refers to any crystal formation that is too minute to be seen with the naked eye.
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Crystal
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In its broadest sense, a crystal is simply an uniform body that has a geometric (consistently shaped) lattice structure. It is the differences between the lattices of various crystals that give rise to their different colours, specific gravities, refraction indices and other physical properties.
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Crystal Face
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Any flat external surface of a crystal.
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Crystallography
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The study of crystal forms is called Crystallography (yes -- with two L's).
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Dispersion
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Refers to the splitting of light into constituent wavelengths of the visible spectrum
(ie. red, orange, yellow, green, blue, indigo and violet).
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Fracture
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Refers to any irregular breakage of a crystal, leaving an uneven surface, without being influenced by the crystal's internal (atomic) structure.
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Gemmology
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The study of gemstones.
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Gemstones
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A collective term, given to pretty much any ornamental stone - whether it be a hard stone, a soft stone, a precious stone, a semi-precious stone... and so on.
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Inclusions
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Any material (whether gaseous, liquid or solid) contained inside a crystal.
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Jewels
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Anything involving a gemstone, particularly that which is ornamental in nature, is counted as a jewel. A jewel will often be a piece of jewellery consisting of gemstones (semi-precious and/or precious) set into a precious metal. But the term can also be applied to gemstones that are unset but are cut.
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Lapidarist
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Someone who cuts and/or polishes gemstones.
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Lattice
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Refers to the shape and nature of the repetitive internal (atomic) structure of a crystal formation.
The lattice structure determines a crystal's hardness and many of its other physical properties.
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Lustre
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A way of describing reflective qualities of the external surface of a crystal.
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Mineralogy
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The study of minerals. It isn't called minerology as some seem to think...
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Minerals
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Minerals are natural solid substances that are found in the earth's crust. They are always non-organic in nature, and most of them have very clear crystal forms. The study of minerals is called Mineralogy (and not minerology as some seem to think).
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Piezo-electric
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The ability of some types of crystal to convert pressure into elecrical discharges, and
to produce consistent physical vibration from electrical impulses.
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Pleochroic
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Refers to those crystals that appear to contain more than one colour or shade,
due to the way in which light reflects differently from the various particles within the crystal.
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Precious Stones
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Also see 'Semi-precious Stones'. All of the 'precious' and 'semi-precious' stones that you'll encounter have some unique or particularly attractive feature; that's what distinguishes them from other stones. If you're wondering how to tell which are more precious than others, I'm afraid that's a bit of a blurred distinction. Long ago, some of today's semi-precious stones were called 'precious'. As times and discoveries pass, so does this definition.
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Refraction
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Refers to the angular 'bending' of light upon entry into a crystal or prism.
Also see 'Refractive Index'.
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Refractive Index
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The measure to which light bends upon entering a particular crystal.
Also see 'Refraction'.
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Rocks
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Often used (slang) in the gemstone trade to refer to Diamonds.
Otherwise, a rock is actually any aggregate of minerals. It may surprise you to hear that, technically speaking, pebbles, gravel and even grains of sand are 'rocks'. Strange... but true.
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Semi-precious Stones
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Refers to gemstones that are nominally of lesser value than the 'precious' categories.
Also see 'Precious Stones'.
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Stones
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As Walter Schumann and Evelyne Stern put it (in the book "Gemstones of the World")... an architect sees it as being the material used for building houses, whilst a jeweller sees it as being a gemstone. Everyone else probably sees it as being a hard lump of combined minerals that you find in the garden.
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Symmetry
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With reference to crystals, their symmetrical natures can be categorised into several
common groups: trigonal, cubic, tetragonal, hexagonal, orthorhombic, monoclinic and triclinic.
All crystals fit into one of these symmetry forms. Anything that doesn't fit... isn't a crystal!
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Synthetics
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Refers to 'crystals' which are man-made, having the same structure and properties as their genuine counterparts.
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