Amethyst
Amethyst usually is a transparent variety of quartz that comes in shades of purple. Some translucent to opaque amethyst is also found and the purplish zones alternate with white or grayish areas. Color zonation can be very intense in transparent, translucent and opaque varieties. Amethyst is the traditional birth stone for the month of February. Quartz in all varieties is Silicon Dioxide, SiO2, it crystallizes in the hexagonal system, it has a specific gravity of 2.66, and it defines 7 on Mohs hardness scale. it has refractive indexes ranging from 1.544 to 1.553, it is uniaxial, positive, and may be strongly dichroic in several colored varieties.
This is how Amethyst looks like:-
