Crystal Systems
There are 7 main crystal systems:

Cubic

Crystals that are essentially cube-shaped, like dice, with three pairs of sides the same length, breadth and height. Some cubic crystals may have developed further into 8- or 12-sided shapes, but these still belong to the cubic system. These crystals are also called isometric crystals. Examples : pyrite and salt.

Monoclinic

One of the most common crystal systems. No pair of faces is the same length, breadth or height as any other. Example : gypsum.

Triclinic

The least symmetrical of the crystal systems. No face has the same dimensions as any other and none of the faces is at right angles to any of the others. Example : axinite.

Tetragonal

This form is more elongated than the cube. The crystals have three faces at right angles to one another, but only two are equal in length, breadth and height. Example : idiocrase.

Orthorhombic

This system has flattened sides that look like table tops. The three faces are unequal, but they are all at right angles to one another. Example : barite.

Hexagonal and Trigonal

These two systems are often grouped together because of their similar shapes. Hexagonal crystals are like cubes with pyramids at top and bottom. Example : beryl. Trigonal crystals are like hexagonal ones, but less clearly defined. Example : quartz.

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