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(from the German Zirkon; original source, Persian zargun, “golden”), a mineral, a nesosilicate with the composition Zr[SiO4]. Distinctions are made between zircons on the basis of impurity content: alvite contains hafnium and thorium, oyamalite contains transition metals and phosphorus, hagathalite contains transition metals and niobium, and naegite contains transition metals, thorium, niobium, and tantalum. Metamict dipyramidal zircons containing thorium, uranium, and water (Th > U) are called malacons, while prismatic zircons (Th < U) are called cyrtolites. Honey yellow, red-brown, and pink transparent zircons are called hyacinths. Metacolloidal, collomorphic zircons are called arshinovites.
Zircon crystallizes in the tetragonal system, forming tabular, short prismatic, or, less often, dipyramidal crystals. Regular concretions with xenotime, YPO4, are frequent. Zircons are brownish yellow to brown, grayish, red, or pink; they may sometimes be colorless. Zircons are transparent to translucent. They usually exhibit no cleavage. Zircons have a hardness of 7–8 on Mohs’ scale and a density of 4,680–4,710 kg/m3 (in the metamict varieties, the hardness and density are less).
Zircon is a characteristic accessory mineral in granites and nepheline syenites and their effusive analogues, as well as of various metamorphic and terrigenous sedimentary rocks; large zircon deposits are found in granitic and alkaline pegmatites. Zircon sometimes concentrates in industrial quantities together with pyrochlore in zones of albitization of alkali rocks. Upon weathering of rocks containing zircon, the mineral may form alluvial deposits. Large reserves of zircon are found in the littoral-marine deposits on the Atlantic coast of the USA (Florida), on the island of Sri Lanka, and in eastern Australia.
Zircon is the major source for the production of zirconium, hafnium, and zirconium oxide (zirconium dioxide). Pure zircon sands are used in mold casting, as well as a starting material in the production of refractories and special ceramic materials. Hyacinth and transparent yellow and green zircons are used in jewelry-making (class II gems).
A. I. GINZBURG