Ex2: Mica has a Foliated (micaceous) Crystal Habit, meaning its habit is to form layers of thin sheets as seen below.
Twinning: When two separate crystals share some of the same crystal lattice points in a symmetrical manner. The result is an intergrowth of two separate crystals in a variety of specific configurations. A twin boundary or composition surface separates the two crystals. Exs:
Cleavage: The tendency of crystalline materials to split along definite crystallographic structural planes. Types of Cleavage: Basal: occurs parallel to the base of the crystal Cubic: occurs parallel to the faces of a cube in a crystal with cubic symmetry. (Ex: grains of table salt) Octahedral: forming octahedral shapes for a crystal with cubic symmetry. Diamond and fluorite exhibit perfect octahedral cleavage. Octahedral cleavage is seen in common semiconductors.