Definition of: crystal

(kris′təl) noun
1. The solid form assumed by many minerals; specifically, colorless transparent quartz, or rock crystal.
2. Physics A homogeneous solid body, exhibiting a definite and symmetrical internal structure, with geometrically arranged cleavage planes and external faces that assume any of a group of patterns associated with peculiarities of atomic structure.
3. Flint glass, or any fine glass, especially as made into high–grade tableware and decorative pieces.
4. A watchglass.
5. A clear, white diamond.
6. A specially shaped and ground piece of quartz or similar material, used to improve radio reception.
—adjective Composed of or like crystal; extremely clear; limpid. [<OF cristal <L crystallum clear ice <Gk. krystallos <krystainein freeze <kryos frost]
—crys·tal·lic (kris·tal′ik) adjective
TYPES OF CRYSTALS
a. Tetragonal pyramid.
b. Tetragonal prism.
c. Dodecahedron.
d. Deltahedron.