About
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.
Crystal Forms & Aggregates
Other ID Marks
Striking Features
Environment
Varieties
✓ common · ✗ uncommon
- Cyrtolite— Variety of Zircon with traces of radioactive elements in its chemical structure. Cyrtolite is a metamict and unstable mineral.
- Jacinth— Yellow, orange, brown, or red variety of Zircon. Also synonym of Hyacinth.
- Jargon— Colorless, pale gray, or pale yellow variety of Zircon.
- Seiland Zircon— Lustrous dark red Zircon from Seiland Island, Norway.
- Starlite— Blue gem variety of Zircon.
Uses
Noteworthy Localities
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 and Lake Clear Townships). 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
Distinguishing Similar Minerals
Cassiterite - Heavier.
Spinel - Zircon in pseudo-octahedral form can be similar, though Spinel is lighter in weight.
Anatase - Slightly different crystal habits, often striated, softer.Monazite - Lower hardness, different crystal forms.
Hafnon - Cannot be distinguished without complex tests.
Photos
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