Amethyst is the birthstone for February and is the purple variety of the mineral Quartz.  Amethyst derives its name from the Greek "amethystos", which means "not drunken".   Amethyst was believed to protect and heal.  

OK, now for the technical gemological information:  Amethyst is silicon dioxide SiO2, Crystal System is Trigonal, Uniaxial Positive, Refractive Index is 1.53to 1.56, DR, 0.009, Specific Gravity is 2.60 to 2.65.

Amethyst can occur in huge flawless crystals and gemstones of all sizes have been faceted. The color of Amethyst is most often caused by iron impurities, though it can also be colored by natural radiation exposure.  Amethyst is sometimes heat treated to deepen the color, or to transform it into Citrine. 

Amethyst is a beautiful stone but not very hard, reaching a 7 on the Mohs Scale (same as a hard steel file).  As a result, amethyst can abrade (scratch) fairly easily.  Avoid leaving amethyst in strong light as the color may fade.