Huge, 11.6" Smoky Quartz Cluster - Brazil
This is a large cluster of dark black, smoky quartz crystals from Brazil. The entire plate is 11.6 inches wide and the longest point is over 5 inches long. The crystals on the specimen are quite large, just about all of which are chip free. The smoky-black coloration goes all the way down to the granite matrix. It has not been heated or treated to change the natural color.
Silicon Dioxide, also know as SiO2 or Quartz, is the second most abundant mineral in the Earth's crust. Quartz crystals generally grow in silica-rich, hot watery solutions called hydrothermal environments, at temperatures between 100°C and 450°C, and usually under very high pressure. Quartz veins are formed when open fissures are filled with hot water during the closing stages of mountains forming, and can be hundreds of millions of years old.
The color of smoky quartz results from free silicon, formed from the silicon dioxide by natural irradiation.