7 Key Terms Flashcards
Aggregate
A solid mass of individual, randomly oriented crystals, intergrown or held together by a natural binding agent.
Cleavage plane
Plane parallel to a possible crystal face, where a diamond can split cleanly when struck.
Covalent bond
A chemical bond formed by two atoms sharing electrons.
Crystal
Solid matter with atoms arranged in a regular, repeating pattern.
Crystalline
Composed of crystals or related to crystals.
Crystal planes
Internal directions parallel to a mineral’s unit cell surfaces.
Crystal shape (form)
Geometric shape of a well-formed crystal.
Crystal structure (lattice)
Regular, repeating arrangement of atoms in a mineral.
Crystal systems
Categories of crystals based on their symmetry and internal structure.
Doubling
The appearance of double images of a gemstone’s facet junctions on the side opposite the viewer.
Doubly refractive (anisotropic)
Possessing different physical or optical properties in different crystal directions.
Glassie
A well-shaped, transparent, octahedral diamond crystal with sharp, square edges.
Glide plane
Crystal distortion caused during growth when one part of the lattice is offset in relation to the rest.
Graining (grain lines)
Visible, shadow-like lines in a diamond caused by irregularities in the crystal structure.
Habit
Characteristic crystal shape of a specific mineral.
Macle
A flat, triangular twinned diamond crystal.
Octahedron
A form with eight (8) equal triangular faces.
Singly refractive (isotropic)
Possessing the same physical or optical properties in all crystal directions.
Specific gravity (SG)
Ratio of the weight of a material to that of an equal volume of water.
Tetrahedron
In diamond, a group of five (5) carbon atoms with one at the center.
Thermal conductivity
The relative ability of a material to transfer heat.
Thermal expansion
Capacity of a material to expand when it’s heated.
Trace elements
Atoms in a gem that aren’t part of its essential chemical composition.
Twinned crystal
Crystal consisting of two or more intergrown crystals with opposing crystal directions.
Unit cell
Smallest group of atoms with the characteristic chemical composition and the basic crystal structure of a mineral.
