Quartz

Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz, several of which are semi-precious gemstones. Throughout the world, varieties of quartz have been since antiquity the most commonly used minerals in the making of jewelry and hardstone carvings.

The quartz group includes a number of different species / varieties. There are two categories crystalline quartz and cryptocrystalline quartz (chalcedony).

Source: en.wikipedia.org/wiki/Quartz

Quartz Properties

Chemical Composition: 
Silica (Silicon Dioxide) SiO2
Colors / Varieties: 
  • Colorless: Rock Crystal
  • Violet: Amethyst
  • Yellow, Golden: Citrine
  • Brown, Grey: Smoky Quartz (Morion)
  • Pink: Rose Quartz
  • Green: Praseolite
  • Rock Crystal with irridescent cracks: Iris Quartz
  • Red Quartz: Rare Variety
  • Blue, green (aventurescent): Aventurine Quartz
  • Quartz Cat's Eye
  • Star Quartz (Six Ray)
  • Parti Color Quartz: Ametrine
  • Sagenitic Quartz (Tourmalinated / Rutilated)
  • Tiger's Eye / Hawk's Eye
  • Milky Quartz
  • Quartzite
Crystal System / Forms: 
Trigonal System
  • Prismatic with pyramidal terminations (rhombohedron, trapezohedron, trigonal, pyramid)
  • Horizontal striations on the prism face, rhomb shaped on rhombohedral face, 'V' shaped markings in twinned crystals.
  • Most quartz is commonly twinned.
  • Types of twinning include Dauphine, Brazil and Japan law twinning.
  • Exhibits both contact and interpenetrant twinning.
Hardness: 
7
Specific Gravity: 
2.63 - 2.68
Cleavage / Fracture: 
No distinct cleavage / conchoidal to uneven fracture.
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).
Lustre: 
Vitreous.
Refractive Index / Birefringence: 
1.544 - 1.553 / 0.009. Range: 1.535 - 1.560
Pleochroism: 
Dichroism - weak to moderate.
Dispersion: 
0.013
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.
U.V. Fluorescence: 
Variable.
Spectrum: 
Green aventurine: bands at 682nm, 649nm
Cause of Color: 
Rose Quartz: Charge transfer reaction (Ti4+ and Fe2+) as a result of irradiation.
Treatment (Enhancement): 
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).
Synthesis: 
Hydrothermal process:
  • Colors - colorless, pink, blue, green, etc.
  • Identification: type of twinning, seed plate, breadcrumb inclusions, Raman / infra-red spectroscopy.
Geological Occurrence: 
Very widespread, in pegmatite.
Sources: 
Brazil, India, South Africa, Namibia, Madagascar, Zambia, Sri Lanka.
Cuts & Uses: 
Facetted cuts, cabochon, carvings, beads, etc.