Zircon | Gemopedia

Radiant zircon is the oldest known gemstone, with some crystals dating back 4 billion years, but also perhaps the most misunderstood. Unfortunately, due to the similarity of zircon's name to the lab created diamond simulant cubic zirconia, many people don't realize that zircon is a beautiful, naturally occurring stone with its own merits. Thanks to its tremendous fire and dispersion, it has been considered a less-expensive stand-in for diamond for many years, although zircon gives us many reasons to sing its praises and appreciate it in its own light.
Alternate Names
High Zircon, Medium Zircon, Low Zircon Or Metamict, Hyacinth, Jacinth, Jargoon Or Jargon, Beccarite, Melichrysos, Sparklite, Starlite, Stremlite
Colors
Colorless, Very Strong Blue To Green-Blue, Yellow, Blue-Green, Yellowish Green, Yellow-Green, Brown, Orangy Yellow To Reddish Orange, Dark Brownish Red, Sometimes Purple,Gray To Bluish Gray,Brownish Gray

Zircon Classification

Common Name

Zircon

Species

Zircon

Variety

Colors

Colorless, Very Strong Blue To Green-Blue, Yellow, Blue-Green, Yellowish Green, Yellow-Green, Brown, Orangy Yellow To Reddish Orange, Dark Brownish Red, Sometimes Purple,Gray To Bluish Gray,Brownish Gray

Alternate Names

High Zircon, Medium Zircon, Low Zircon Or Metamict, Hyacinth, Jacinth, Jargoon Or Jargon, Beccarite, Melichrysos, Sparklite, Starlite, Stremlite

Gemstone Groups

Key Separations

Zircon exhibits strong doubling, easily observed using a 10x loupe as a doubling of back facet edges. The refractive index of zircon is over the limit of the standard gemological refractometer. Spectrum should show a distinct line at 653.5nm, but possibly up to 40 lines. Low type zircon's spectra might have fuzzy lines and not well defined. OTL RI reading, eye visable doubling and spectrum. Some low type zircon appears to be SR and amorphous.

Comments

Zircon affected by natural radiation may have altered crystal lattice structure that can affect some of its measurable properties. Crystals are prismatic in a tetragonal form, often with bipyramidal terminations, with square or rectangular cross-sections. Always look for doubling in 3 directions.Misnomers: Colorless zircon- Matara diamond, Blue zircon- Siam aquamarine.High and medium zircon: transparent colorless, blue, yellow to yellow-green, brownish green, orange to brown, brownish to orangy red.Low or metamict zircon: transparent brownish to yellowish green with a cloudy texture; more rarely brown to orange.Hyacinth or jacinth: yellow-red, orange, red-brown to brown.Jargoon or jargon: light yellow to colorless stones that do not show the red color of hyacinth. Traditionally they are stones from Sri Lanka.Beccarite: green zircon that displays optical properties. Melichrysos: straw yellow.Starlite or stremlite: blue heat treated zircon.Sparklite: colorless zirconHigh type RI: 1.925 to 1.984(+/-0.040); Medium type RI: 1.875 to 1.905(+/-0.030); Low type RI: 1.810 to 1.815 rarely under 1.800Low type has low birefringence and high type has high birefringence. Blue is created by heating reddish brown stones.The green metamict zircon might be slightly radioactive.

Zircon Optical Properties

Transparency

Transparent

Refractive Index

Over the Limit 1.81-2.024

Birefringence

0.002-0.059

Optic Character

Uniaxial

Optic Sign

Positive

Polariscope Reaction

Doubly Refractive (DR)

Fluorescence

SWUV: Variable
LWUV: Variable

CCF Reaction

Blue: greenish; Green: sometimes pinkish

Pleochroism

Dichroic, (in blue gems) strong blue and colorless; (in red gems) moderate purplish red and reddish brown

Dispersion

Strength: moderate fire Value: 0.038

Comments

Zircon Chemistry & Crystallography

Chemical Name

zirconium silicate

Chemical Formula

ZrSiO4

Synthesis

Crystal System

Tetragonal

Classification

Silicate

Nature

Natural

Crystallinity

Crystalline

Comments

Zircon Characteristic Physical Properties

Hardness

6.5-7.5

Streak

White

Specific Gravity

3.9-4.73

Toughness

Varies

Inclusions

Blue and colorless zircons have Type I clarity. Orange, yellow, red and green zircons are Type II clarity stones. Stone might have needles and liquid inclusions. Stones might have abrasions on facet edges. Blue and white stones might show small white billowy inclusions. Low type green stones typically have a lower polish luster and often show strong parallel color zoning or repeated twinning planes, might show hazy appearance when viewed with illumination and angular "skeletal-like" tension fissures.

Luster

Bright Vitreous

Stability

Fair

Fracture

Conchoidal

Cleavage

None

Comments

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