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Colored Stones 3
Gems & their Physical Properties
32
Language - Other
Post-Graduate
05/15/2018

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Cards

Term
Unit Cell
Definition
the smallest group of atoms with both the characteristic chemical composition and crystal structure of a mineral
Term
Aggregate
Definition
a mass of tiny, randomly oriented crystals
Term
Microcrystalline
Definition
an aggregate made up of individual crystals visible under magnification
Term
Cryptocrystalline
Definition
an aggregate made up of individual crystals detectable only under very high magnification
Term
Twinning
Definition
change in a gem's crystal direction during or after growth
Term
Twinning Plane
Definition
location of a change in crystal growth direction
Term
Penetration Twinning
Definition
when twinned crystals look as though two crystals have grown through one another
Term
Cyclic Twinning
Definition
when twinning planes aren't parallel and results in a wheel-shaped crystal
Term
Polysynthetic 'Lamellar' Twinning
Definition
the boundaries between the twinned crystals are parallel
Term
Inclusions
Definition
a characteristic enclosed within a gemstone, or reaching its surface from the interior
Term
Two-Phase Inclusion
Definition
a hollow cavity in a gem, usually filled with a liquid and a gas
Term
Three-Phase Inclusion
Definition
a hollow cavity in a gem filled with a liquid, a gas, and one or more crystals
Term
Trace Elements
Definition
atoms in a gem that aren't part of its essential chemical composition
Term
Habit
Definition
the characteristic external crystal shape or form of a mineral
Term
Tabular
Definition

squat and flat

 

Ex) ruby crystal

Term
Prism/Prismatic
Definition

columnar, with 3, 4, 6, 8, or 12 parallel faces

 

Ex) aquamarine

Term
Euhedral
Definition
well formed, with sharp crystal faces
Term
Anhedral
Definition
lacking obvious crystal faces
Term
Striations
Definition
horizontal or vertical growth markings on a crystal
Term
Pyramind
Definition
shape with equal triangular faces that meet at a point
Term
Bipyramid
Definition
shape with two pyramids back to back
Term
Density
Definition
how heavy an object is relative to its size
Term
Specific Gravity
Definition
ratio of the weigh of a material to the weight of an equal volume of water
Term
Durability
Definition
a combination of hardness, toughness, and stability
Term
Hardness
Definition
how well a gem resists scratches
Term
Toughness
Definition
how well a gemstone resists breaking and chipping
Term
Cleavage
Definition
a smooth, flat break in a gemstone parallel to planes of atomic weakness, caused by weak or fewer bonds between atoms, or both
Term
Parting
Definition
a flat break in a gemstone caused by concentrated included minerals parallel to a twinning plane
Term
Fracture
Definition
any break in a gem other than cleavage or parting
Term
Conchoidal Fracture
Definition
a curved and ridged fracture in a gemstone, extending from the surface inward
Term
Stability
Definition
how well a gemstone resists light, heat, and chemicals
Term
Thermal Shock
Definition
damage caused by sudden, extreme temperature changes
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