The basic systems are isometric, tetragonal, hexagonal, orthorhombic, monoclinic, and triclinic. Isometric crystals generally have symmetrical faces, and are characteristically cubes, octahedrons, dodecahedrons, etc. Isometric crystals have three axes of symmetry that are all at right angles to each other. The axes are all of equal length. An example of a mineral with crystals in the isometric system is pyrite, which can form into nearly perfect cubes.
Tetragonal crystals are often long and slender, or can even look like a needle.
The crystals in this system characteristically form 4-sided prisms, pyramids, and dipyramids. The third axis is either longer or shorter than the other two, and is at right angles to them. Chalcopyrite Hexagonal crystals are usually prismatic or columnar, and they typically have hexagonal or triangular-like cross sections. They may form 3 or 6 sided prisms, pyramids, and rhombohedrons. The trigonal system is very similar, and often included in the hexagonal system.