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Single Dark-Red Zircon Crystal

The Mineral zircon




Zircon is a well-known mineral that makes an important gemstone of of many colors. Its brilliant luster and fire, combined with good hardness, make it a desirable gem. Natural Zircon with good color and transparency is uncommon; most Zircon crystals are opaque and brownish. However, most Zircon gemstones, especially the blue and white forms, are enhanced by heat treatment.

Zircon often contains traces of radioactive elements in its structure, which causes it to be metamict. This unstable form of Zircon, called Cyrtolite, is characterized by rounded, almost dome-shaped crystals which are dull or pitchy in luster. When heated, these metamict Zircon crystals become stable, and revert to their normal crystal structure. Radioactive Zircon that has undergone a metamiction process is sometimes called "Low Zircon", and stable Zircon with an intact crystal lattice "High Zircon".

The dark brown to black color observed in most Zircon crystals is caused from iron oxide impurities. The green coloring in many rounded pebbles usually indicates the Zircon is radioactive variety. An interesting habit occasionally exhibited in Zircon from a few localities is that their color darkens and their luster dulls upon prolonged exposure to sunlight. This effect can be reversed by giving the stones a second heat treatment.

For additional information, see the gemstone section on
Zircon.

Chemical Formula ZrSiO4
Composition Zirconium silicate, often with some hafnium and occasionally with some uranium, thorium, and yttrium. It can contain up to 20 percent of hafnium in its structure; if it exceeds that amount then it is no longer Zircon but Hafnon.
Variable Formula (Zr,Hf)SiO4 ;
(Zr,Hf,U,Th,Y)SiO4
Color The most common color is dark brown. Also black, gray, light brown, brownish-red, orange, pink, yellow, light blue, light green, light purple white, and colorless. Sometimes multicolored black and dark red, or multicolored with lighter and darker streaks.
Streak Colorless
Hardness 7.5
Crystal System Tetragonal
3D Crystal Atlas
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Crystal Forms
and Aggregates
As short and stubby crystals, as well as prismatic which are sometimes elongated. Crystals are almost always terminated with a pyramidal termination. Crystals may be doubly terminated, and occasionally entirely pyramidal resembling an octahedron. Also grainy, as fibrous aggregates, and as rounded, waterworn pebbles. Twinned Zircon crystals are uncommon but do exist. Crystals can also be in a metamict where they exhibit rounded crystal faces.
Transparency Transparent to opaque
Specific Gravity 4.6 - 4.8
Luster Greasy to adamantine. Radioactive Zircon has a pitchy luster.
Cleavage 3,2
Fracture Conchoidal to uneven
Tenacity Brittle
Other ID Marks May be fluorescent orange-yellow in shortwave ultraviolet light.
In Group Silicates; Nesosilicates
Striking Features Crystal shape, hardness, and weight
Environment Most often in igneous environments, usually in granite pegmatites and in nepheline syenite pegmatites. Also in high-grade metamorphic rocks and in placer deposits.
Rock Type Igneous, Metamorphic
Popularity (1-4) 1
Prevalence (1-3) 2
Demand (1-3) 1

Zircon ON EBAY

VARIETIES
 -  Variety of Zircon with traces of radioactive elements in its chemical structure. Cyrtolite is a metamict and unstable mineral.
 -  Yellow, orange, brown, or red variety of Zircon. Also synonym of Hyacinth.
 -  Colorless, pale gray, or pale yellow variety of Zircon.
 -  Lustrous dark red Zircon from Seiland Island, Norway.
 -  Blue gem variety of Zircon.

USES
Zircon is an important gemstone, with several color forms used in various forms of jewelry. Zircon is also the most significant ore of the element zirconium, and it is also the most important ore of the rare element hafnium, which can be present in considerable quantities in Zircon. In several localities, Zircon is also an ore of the radioactive element thorium.

NOTEWORTHY LOCALITIES
Many good localities for Zircon are known worldwide. In Russia, excellent Zircon specimens come from the Lovozero Massif in the Kola Peninsula; and at Vishnevye in the Ural Mountains. Sharp, lustrous brownish-red crystals come from Pakistan in Gilgit, Chilas, and Harchu; and crystals of similar quality from Darra-i-Pech, Nangarhar Province, Afghanistan. Transparent gemmy green and brown Zircon comes from Mogok, Burma (Myanmar); and large elongated crystals from the Giant Crystal Quarry, Ratnapura, Sri Lanka.

Important European Zircon localities include Store Kufjord, Seiland Island, Norway (famous for its fabulous transparent dark red crystals); the Nibbio mine, Mergozzo, Piedmont, Italy; the alluvials of Rochefort-Montagne, Puy-de-Dôme, Auvergne, France; and the Laach lake volcanic complex, Eifel Mts, Germany (as strangely-colored white and light yellow crystals).

Large, dull crystals come from Mud Tank in the Harts Ranges, Northern Territory, Australia; and short, stubby pyramidal crystals from Peixe, Goias, Brazil. Outstanding cream-colored Zircon crystals come from Mount Malosa, Zomba Region, Malawi; and large crystals have come from several of the Madagascar pegmatites, especially in the Amboasary District, Tuléar Province.

In Canada, one of the most exceptional Zircon localities is the Bancroft District, Hastings Co., Ontario (especially in Dungannon Township). Large, well formed crystals are famous from Tory Hill, Wilberforce, Haliburton Co., Ontario. Lustrous sharp crystals come from the famous Poudrette quarry, Mont Saint-Hilaire, Québec; and large crystals from the Kipawa Alkaline complex, Lac Sheffield, Témiscamingue, Québec.

In the U.S., one of the most important localities is the Eureka Tunnel, St. Peters Dome, Cheyenne District, El Paso Co., Colorado. Very good Zircon crystals come from Pacoima Canyon in the San Gabriel Mts, Los Angeles Co., California; and an old Zircon locality that once produced fine large crystals is the Wichita National Wildlife Refuge near Indiahoma, Comanche Co., Oklahoma. Doubly terminated gray floater crystals come from Zirconia and Tuxedo, Henderson Co., North Carolina. Massive Cyrtolite comes from Spruce Pine, Mitchell Co., North Carolina; and large sharp crystals from the Tigerville Prospect, Greenville Co., South Carolina.

COMMON MINERAL ASSOCIATIONS
Albite, Quartz, Biotite, Chlorite, Orthoclase, Nepheline, Monazite, Xenotime, Aegirine, Garnet

DISTINGUISHING SIMILAR MINERALS
Vesuvianite - Softer (6½), lighter in weight.
Cassiterite - Heavier.
Spinel - Zircon in pseudo-octahedral form can be similar, though Spinel is lighter in weight (3.5 - 4.1).
Anatase - Slightly different crystal habits, often striated, softer.
Hafnon - Cannot be distinguished without complex tests.


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