7 Key Terms

Question 1

Aggregate

Answer 1

A solid mass of individual, randomly oriented crystals, intergrown or held together by a natural binding agent.

Question 2

Cleavage plane

Answer 2

Plane parallel to a possible crystal face, where a diamond can split cleanly when struck.

Question 3

Covalent bond

Answer 3

A chemical bond formed by two atoms sharing electrons.

Question 4

Crystal

Answer 4

Solid matter with atoms arranged in a regular, repeating pattern.

Question 5

Crystalline

Answer 5

Composed of crystals or related to crystals.

Question 6

Crystal planes

Answer 6

Internal directions parallel to a mineral’s unit cell surfaces.

Question 7

Crystal shape (form)

Answer 7

Geometric shape of a well-formed crystal.

Question 8

Crystal structure (lattice)

Answer 8

Regular, repeating arrangement of atoms in a mineral.

Question 9

Crystal systems

Answer 9

Categories of crystals based on their symmetry and internal structure.

Question 10

Doubling

Answer 10

The appearance of double images of a gemstone’s facet junctions on the side opposite the viewer.

Question 11

Doubly refractive (anisotropic)

Answer 11

Possessing different physical or optical properties in different crystal directions.

Question 12

Glassie

Answer 12

A well-shaped, transparent, octahedral diamond crystal with sharp, square edges.

Question 13

Glide plane

Answer 13

Crystal distortion caused during growth when one part of the lattice is offset in relation to the rest.

Question 14

Graining (grain lines)

Answer 14

Visible, shadow-like lines in a diamond caused by irregularities in the crystal structure.

Question 15

Habit

Answer 15

Characteristic crystal shape of a specific mineral.

Question 16

Macle

Answer 16

A flat, triangular twinned diamond crystal.

Question 17

Octahedron

Answer 17

A form with eight (8) equal triangular faces.

Question 18

Singly refractive (isotropic)

Answer 18

Possessing the same physical or optical properties in all crystal directions.

Question 19

Specific gravity (SG)

Answer 19

Ratio of the weight of a material to that of an equal volume of water.

Question 20

Tetrahedron

Answer 20

In diamond, a group of five (5) carbon atoms with one at the center.

Question 21

Thermal conductivity

Answer 21

The relative ability of a material to transfer heat.

Question 22

Thermal expansion

Answer 22

Capacity of a material to expand when it’s heated.

Question 23

Trace elements

Answer 23

Atoms in a gem that aren’t part of its essential chemical composition.

Question 24

Twinned crystal

Answer 24

Crystal consisting of two or more intergrown crystals with opposing crystal directions.

Question 25

Unit cell

Answer 25

Smallest group of atoms with the characteristic chemical composition and the basic crystal structure of a mineral.