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Classes of Crystals

There are four systems of crystals with various classifications. Every classification has a certain amount of faces that appear on the crystal and typically describes the symmetry and characteristics of the particular class. The crystal may resemble a cube, pyramid, cone or a host of other shapes.

Pedial Class
- The Pedial Class is apart of the Triclinic System which characterizes crystal with one fold axis. This crystal class has different face on each side. No symmetry exists in the Pedial Class. This is rare class, since most minerals have at least two face.
Pinacoidal Class
- In the Pinacoidal Class, the crystal has symmetry only through the centerpiece and two faces. When faces sit in this manner, many refer to this crystal as pinacoids. Some mineral in this class include wollastonite, plagioclase and turquoise. In addition, the Pinacoidal Class is apart of the Triclinic System.
Tetragonal-Pyramidal Class
- The Tetragonal-Pyramidal Class features four-fold axis. It does not have planes facing each other, nor does a face sit on the bottom. The only mineral in this classification is Wulfinite. This is apart of the Tetragonal System.
Rhombic-disphenoidal Class
- The Rhombic-disphenoidal Class of crystal is part of the Orthorhombic System. This system feature crystal features two-fold axis. In addition, the Rhombic Class has three perpendicular two-fold axis and two parallel planes. The disphenoid faces that identify this class include two faces on the upper and lower section of the crystal that are 90 degrees apart. A mineral of the Rhombic-disphenoidal is the Epsomite.

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