What Are the Different Kinds of Crystals?

Cubic Crystals

• Cubic crystals are usually shaped like a cube with six sides, which are all shaped like squares and overlap one of the axes of the crystal. Cubic crystals sometimes form with eight or 10 faces. Eight-faced cubic crystals are known as octahedrons and 10-faced cubic crystals are known as dodecahedrons. Some examples of cubic crystals include diamonds, garnet and spinel.

Hexagonal Crystals

• Hexagonal crystals form with six sides. Only three of the six sides are the same length. The crystals are prisms with hexagonal shapes at the ends. Some examples of hexagonal crystals are aquamarines, beryl, emeralds and heliodors.

Monoclinic Crystals

• Monoclinic crystals have axes that are all different lengths, with two of them meeting at a 90-degree angle. Monoclinic can often form in shapes similar to pyramids and prisms. Some examples of monoclinic crystals include azurite, feldspar, kunzite and nephrite.

Orthorhombic Crystals

• Orthorhombic crystals have axes that are each different lengths, with all of them meeting at a 90-degree angle. Some examples of orthorhombic crystals include alexandrite, iolite, tanzanite and topaz.

Tetragonal Crystals

• The axes of tetragonal crystals also meet at a 90-degree angle. Two of the three axes are the same length, while the third is longer than both of the others. A zircon gemstone is one example of a tetragonal crystal.

Triclinic Crystals

• Triclinic crystals have axes that are all different lengths, with none of them meeting at a 90-degree angle, which is common for other types of crystals. Triclinic come in various odd shapes that tend to have asymmetrical sides. A turquoise is one example of a triclinic crystal.

Trigonal Crystals

• Trigonal crystals are a sub-system of hexagonal crystals and are often classified as hexagonal. However, the difference between regular hexagonal crystals and trigonal crystals is that the trigonal crystals have three-fold axes, while the hexagonal crystals have six-fold axes. Some examples of trigonal crystals include citrine, corundum, ruby, tourmaline and quartz.