Citrine is the yellow or golden yellow variety of quartz. The yellow coloration, due to the presence of iron, is also responsible for the name, derived from the word “citrus”. Natural citrine is usually a pale yellow, but rare; most citrine on the market is heat-treated amethyst.

Gem-quality citrine is extremely rare. The best material is found in Brazil, Spain, Madagascar, and the former USSR.

Citrine has been used to imitate topaz and was once called Brazilian topaz.

Chemical Composition: 

Silica (Silicon Dioxide) SiO₂

Colors / Varieties: 

Yellow, Golden

Crystal System / Forms: 

Trigonal System

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: 

Yellow / Slightly paler yellow

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: 

Not characteristic.

Cause of Color: 

Trace of Iron (Fe³⁺)

Treatment (Enhancement): 

• Coating: all colors, thin film of gold on colorless will give a blue color (aqua aura).
• Colorless impregnation: with oil or resin to improve clarity.
• Colored impregnation (dyeing): all colors, quartzite
• Heat Treatment:
  1. Light yellow to deeper yellow
• Irradiation:
  1. Citrine to amethyst

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:

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

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.)

Geological Occurrence: 

Very widespread, in pegmatite.

Sources: 

Brazil, India, South Africa, Namibia, Madagascar, Zambia, Sri Lanka.

Cuts & Uses: 

Facetted cuts, cabochon, carvings, beads, etc.