Introduction
Color
Streak
Transparency
Luster
Hardness
Cleavage
Fracture
Specific Gravity
Crystal Form
Mineral Matters
Regional Minerals

Crystal Form
Minerals grow in specific shapes, and usually crystallize into one of six crystal systems. The axes of the crystal, the angles at which the axes intersect, and the degree of symmetry define each system.
Isometric  Also called the cubic crystal system. Crystals are usually shaped like blocks, with similar and symmetrical faces. The crystal has three axes of symmetry, all at right angles to each other, and all of the same length. Example: pyrite.
Tetragonal  Typically, the crystals are shaped like foursided prisms and pyramids. Each crystal has three axes, all perpendicular to one another. Two axes are the same length and lie on a horizontal plane. The third axis is not the same length and is at a right angle to the other two.
Example: zircon.
Hexagonal  These crystals are usually shaped like sixsided prisms or pyramids. Each crystal has four axes of symmetry. Three lie in the same plane, are the same length, and intersect at 120° angles. The fourth axis is not the same length, and is perpendicular to other three.
Example: beryl.
Orthorhombic  These crystals are short and stubby. Each crystal has three unequal axes, all at right angles to one another.
Example: topaz
Monoclinic  Crystals are short and stubby with tilted faces at each end. Each crystal has three unequal axes. Two axes lie in the same plane at right angles to each other. The third axis is inclined.
Example: gypsum.
Triclinic  Crystals are usually flat with sharp edges, but exhibit no right angles. Each crystal has three unequal axes. None are perpendicular to one another.
Example: feldspar.
