Cause of Color :
Trace of Iron (Fe3+
Chemical Composition :
Silica (Silicon Dioxide) SiO2
Crystal System / Forms :
Cuts & Uses :
Facetted cuts, cabochon, carvings, beads, etc.
Liquid and two phase, color zoning, negative crystals, zebra-stripe finger prints (structural), crystal inclusions, green fuchsite mica flakes / platelets in aventurine quartz, rutile / tourmaline needles in sagenitic quartz. Brazil law twinning is seen in natural quartz.
Optic Character :
Anisotropic, D.R.; Uniaxial positive. May exhibit a bull’s eye optic figure (quartz rotates the plane of polarisation parallel to the c-axis).
Yellow / Slightly paler yellow
Refractive Index / Birefringence :
1.544 – 1.553 / 0.009. Range: 1.535 – 1.560
Simulants (with separation tests) :
Scapolite (optic figure/sign, U.V. fluorescence, inclusions, doubling), synthetic citrine (inclusions, infra red spectroscopy), beryl (optic figure/sign, inclusions, R.I.), topaz (optic figure, R.I., S.G.)
Brazil, India, South Africa, Namibia, Madagascar, Zambia, Sri Lanka.
Specific Tests :
- Piezoelectric: develops an electric charge when pressure is applied.
- Pyroelectricity: develops an electrical charge when heated.
- Diasterism in star variety (star visible in reflected and transmitted light).
- Identification: type of twinning, seed plate, breadcrumb inclusions, Raman / infra-red spectroscopy.