Specific Gravity: 2-2,20
Crystal System: amorphous materia
Index of Refraction : 1,430-1,460
Transparency: from nearly translucent to opaque
Quartz is composed of a hydrated silicon gel. color ranges are white, grey, blue, green, orange, pink, and black. There are three varieties of Opal: Common Opal, transparent Fire Opal (yellow, orange, and red), and Precious Opal, characterized by a play-of-color known as Mosaic or Arlequin.
Mining sites are located in Australia, Mexico, Nevada (U.S.A), Sri Lanka..