A Quartz and Amethyst Crystal

A quartz (clear) and amethyst (purple). Amethyst is a purple form of quartz.

Crystals are often used in spell casting, often for focusing energy or perhaps representing the earth element. They are also quite pretty.

Note that real crystals, even small ones, typically have some small flaws. These crystals have tiny imperfections, and you can clearly see where they were detached at the base from the larger stone they had formed on.

Clear crystals may be made of glass and not true quartz. If a crystal looks too perfect to be quartz, has no flaws at it's base, and has small air bubbles it may well be glass.