Formula: Zr(SiO4)
Nesosilicate (insular SiO4 groups) of zirconium


Alvite is a metamict, often hafnium-rich variety of zircon from granite pegmatites
Cyrtolite is a hydrous thorium and uranium bearing variety of zircon


Specific gravity: 4.6 to 4.7
Hardness: 7½
Streak: White
Colour: Brown, reddish-brown, colourless, grey, green. The blue colour of some zircon is caused by quadrivalent uranium U4+ (Mindat)
Solubility: Insoluble in hydrochloric, sulphuric and nitric acid
Common impurities: Hf,Th,U,Rare Earth Elements,O,H,H2O,Fe,Al,P.

Plutonic igneous environments (common)
Pegmatites (common)
Placer deposits
Sedimentary environments
Metamorphic environments (less common)

Zircon is a common and widely distributed primary mineral in granite and granite pegmatites, and placers. It is less common in metamorphic rocks, but may be found in gneiss after surviving regional metamorphism (Lauf p62). Because it is hard and chemically stable, zircon is a common accessory mineral in sediments.

Zircon is common in nepheline syenite, and it also may be found in granite, granodiorite, diorite, monzonite, rhyolite, limestone, gneiss, schist, andesite and phyllite.

Because zircon is one of the few minerals that can accommodate large tetravalent ions in its structure, it often contains the radioactive elements uranium and thorium (Lauf p61-62).


At the Mud Tank Zircon Field, Alcoota Station, Central Desert Region, Northern Territory, Australia, gem quality zircon is found in weathered carbonatite. This zircon is unusual in that it contains almost no radioactive trace elements.
Mud Tank zircons are a mineralogical curiosity because they can be extremely large and they come from a carbonatite. The Mud Tank deposit is unique as the only known carbonatite containing gem-quality zircon. The general and accessory mineralogy of the deposit includes biotite, albite, amphiboles, pyrite, chalcopyrite and phlogopite — the last identified as hydrobiotite. The majority of the carbonatite at depth consists of small flakes of biotite in a fine-grained matrix of dolomite, calcite, apatite and amphiboles with occasional but scarce small zircon and magnetite/martite crystals.
Zircon occurs as huge single crystals to 40 cm in size, but is more commonly found as small crystals under 2 or 3 cm, broken crystal fragments, rounded water-polished pebbles and abraded fragments of crystals. Generally, zircon is found loose in gravels and rarely in chunks of secondary and tertiary matrix; actual samples of unaltered carbonatite are very rare and, like zircon, they have usually been preserved by encapsulation in tertiary calcite. It seems that the primary zircon matrix was a coeval crystallisation of fluorapatite and magnetite, with the latter now partially altered to martite.
Later-developed matrix includes compact limestone, silica replacing carbonate, or a crumbly aggregate of magnetite/martite, goethite, limonite and secondary calcite, with apatite. Even when found isolated in gravels, zircon is usually covered by iron oxides and a tightly adhering film of gypsum. All large Mud Tank zircon crystals show evidence of late-stage growth forming “boiler-plate” or “paddy field” corrugations on pyramidal faces.
A large fractured, red-brown, single crystal of zircon weighing 32 kg has been found. It was originally doubly terminated, and contained transparent gemmy material (Minrec 51.6.815-824).

At the John Dole quarry, near Bancroft, Ontario, Canada, zircon is associated with fergusonite (Lauf p68).

At Girardville, Quebec, Canada, zircon is enriched in hafnium (R&M 88.5.432).

At the placer gold mines at Dawson, the Yukon, Canada, zircon is associated with gold (R&M 85.1.41).

At Bo Loei in Cambodia, zircon is enriched with uranium and thorium.

At Mt Malosa, Zomba district, Malawi, zircon occurs in alkaline rocks associated with aegirine, arfvedsonite and feldspar (Lauf p66).

At Palabora, South Africa, zircon is associated with phlogopite and calcite (R&M 92.5.449-450).

In Swaziland, zircon is associated with beryl in granite pegmatites (R&M 85.5.451).

Amity, Town of Warwick, Orange county, New York, USA, is an area of granite intrusions into marble and associated gneiss. The marble is mostly composed of white crystalline calcite that often has small flakes or spheres of graphite and phlogopite. Zircon occurs occasionally as individual dark brown tetragonal prisms in massive scapolite. The prism is terminated by a tetragonal pyramid and may be as large as 1.5 cm (R&M 96.5.441).

The Purple Diopside Mound, Rose Road, Pitcairn, St. Lawrence county, New York, USA, is situated in marble. The development of veins of large crystals probably occurred as a result of fluid penetration from a concurrent intrusion. Many of the minerals of interest to collectors formed during this primary event, with additional species resulting from the subsequent alteration of scapolite. There seems to be little, if any, secondary, late-stage mineralisation present.
Zircon crystals are relatively common as inclusions in scapolite, but they require an SEM to observe them. (R&M 96.6.552).

At Tigerville, Greenville county, South Carolina, USA, zircon occurs in a pegmatite in a matrix of partly altered microcline, riebeckite and anatase (Lauf p66).

At the Nine Mile granite pegmatite, Marathon County, Wisconsin, USA, zircon is a common accessory mineral, exhibiting late-stage enrichment with hafnium. Zircon with closely associated albite is probably one of the last minerals to form in the pegmatite. Other associated minerals include cassiterite, columbite and pyrochlore.

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