Smoky Quartz

smoky-quartz
Smoky Quartz

Smoky quartz includes quartz of a light brown or dark brown colour, greyish brown quartz, and the black variety called morion. Brown or smoky quartz from the Cairngorm Mountains of Scotland is called cairngorm. When irradiated, colourless quartz may change colour to greyish brown, suggesting that brown quartz may have been formed by natural radiation within the ground. Brown quartz crystals are hexagonal prisms with pyramidal ends, in which inclusions of the mineral rutile may be present.

Crystals weighing as much as 300kg have been found in Brazil. Other localities include Madagascar, the Swiss Alps, Colorado (USA), Australia and Spain.

Much of the smoky quartz on the market is in fact irradiated rock crystal. Smoky quartz has been confused with andalusite, axinite, idocrase, and brown tourmaline.

Smoky Quartz Pictures

Smoky quartz crystalsPolished smoky quartz crystals in displaySmoky quartz found in Swiss Alps

Cause of Color :

Color center due to the presence of aluminium.

Chemical Composition :

Silica (Silicon Dioxide) SiO2

Crystal System / Forms :

Trigonal System

Cuts & Uses :

Facetted cuts, cabochon, carvings, beads, etc.

Dispersion : 0.013
Hardness : 7
Lustre : Vitreous
Magnification :

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).

Pleochroism : Brown / Reddish brown
Refractive Index / Birefringence :

1.544 – 1.553 / 0.009. Range: 1.535 – 1.560

Simulants (with separation tests) :

Synthetic quartz (inclusions, infra-red spectroscopy), glass (optic character), zoisite (R.I., S.G.), tourmaline (R.I., S.G., inclusions), natural spinel (optic character)

Sources :

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).
Spectrum :

Not characteristic.

Synthesis :

Hydrothermal process:

  • Identification: type of twinning, seed plate, breadcrumb inclusions, Raman / infra-red spectroscopy.

Reader Interactions

Leave a Reply