No regular atomic structure. No tendency to assume a definite external shape. Properties which are the same in all directions. Possesses the regular structure and directional properties of a crystal but not the regular geometrical shape. Also called massive.
Different species vary in the symmetrical arrangement of faces.
These arrangements have certain 'planes' and 'axes' of symmetry. These form part of the definition of the crystal system to which specific gemstones belong. An imaginary plane dividing a body into two parts such that each is the reflected image of the other. Crystals may have more than one plane of symmetry. Often present, it exists when every face of a perfect crystal is exactly opposite a similar face on the other side of the crystal.