Term
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Definition
| the smallest group of atoms with both the characteristic chemical composition and crystal structure of a mineral |
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Definition
| a mass of tiny, randomly oriented crystals |
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Term
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Definition
| an aggregate made up of individual crystals visible under magnification |
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Term
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Definition
| an aggregate made up of individual crystals detectable only under very high magnification |
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Term
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Definition
| change in a gem's crystal direction during or after growth |
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Term
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Definition
| location of a change in crystal growth direction |
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Term
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Definition
| when twinned crystals look as though two crystals have grown through one another |
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Term
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Definition
| when twinning planes aren't parallel and results in a wheel-shaped crystal |
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Term
| Polysynthetic 'Lamellar' Twinning |
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Definition
| the boundaries between the twinned crystals are parallel |
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Term
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Definition
| a characteristic enclosed within a gemstone, or reaching its surface from the interior |
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Term
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Definition
| a hollow cavity in a gem, usually filled with a liquid and a gas |
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Term
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Definition
| a hollow cavity in a gem filled with a liquid, a gas, and one or more crystals |
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Term
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Definition
| atoms in a gem that aren't part of its essential chemical composition |
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Term
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Definition
| the characteristic external crystal shape or form of a mineral |
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Term
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Definition
squat and flat
Ex) ruby crystal |
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Term
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Definition
columnar, with 3, 4, 6, 8, or 12 parallel faces
Ex) aquamarine |
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Term
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Definition
| well formed, with sharp crystal faces |
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Term
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Definition
| lacking obvious crystal faces |
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Term
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Definition
| horizontal or vertical growth markings on a crystal |
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Term
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Definition
| shape with equal triangular faces that meet at a point |
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Term
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Definition
| shape with two pyramids back to back |
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Term
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Definition
| how heavy an object is relative to its size |
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Term
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Definition
| ratio of the weigh of a material to the weight of an equal volume of water |
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Term
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Definition
| a combination of hardness, toughness, and stability |
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Term
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Definition
| how well a gem resists scratches |
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Term
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Definition
| how well a gemstone resists breaking and chipping |
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Term
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Definition
| a smooth, flat break in a gemstone parallel to planes of atomic weakness, caused by weak or fewer bonds between atoms, or both |
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Term
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Definition
| a flat break in a gemstone caused by concentrated included minerals parallel to a twinning plane |
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Term
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Definition
| any break in a gem other than cleavage or parting |
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Term
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Definition
| a curved and ridged fracture in a gemstone, extending from the surface inward |
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Term
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Definition
| how well a gemstone resists light, heat, and chemicals |
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Term
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Definition
| damage caused by sudden, extreme temperature changes |
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