Citrine
Citrine is a light yellow to yellowish-brown variety of QUARTZ. Natural citrine is colored by trace amounts of ferric hydroxide. Most of the citrine on the market is actually heat-treated amethyst or smoky quartz.
As in other varieties of quartz, citrine has a hardness of 7, a specific gravity of 2.65, and chemically, is SiO2. It has a vitreous luster and belongs to the hexagonal crystal system.
When amethyst is heated to approximately 500-600 degrees C, a yellowish-brown citrine color is produced. Not all amethyst responds in like fashion. Most of the Brazilian citrine on the market comes from the Irai region of Rio Grande do Sul.
Chemistry: SiO2 ♦ Variety: quartz ♦ transparent to translucent ♦ Luster: vitreous ♦ Crystal system: hexagonal ♦ Moh's hardness: 7 ♦ Color: yellow to orange ♦ Localities: world-wide, but principally Brazil