Description
The mineral zircon is a zirconium silicate with the chemical formula ZrSiO4. It belongs to the nesosilicate family. The natural color of zircon ranges from colorless, golden yellow, and red to brown. Zircon should not be confused with the synthetic gemstone cubic zirconia, which is a popular imitation of diamonds. Since the advent of radiometric dating, zircons have been of particular interest to geologists. Zircons generally contain small amounts of radioactive isotopes 23 (from 10 ppm to 5 percent by mass). All of these isotopes eventually decay into an isotope of lead. By determining the uranium/lead or thorium/lead ratio of the respective isotopes, one can determine the crystallization time of the crystal and thus the age of the rock in which it is found. Zircons are exceptionally resistant to weathering and even extreme metamorphism; they can even record information about these types of events in their isotope ratios. The name zircon can be traced back to the Persian zargūn, meaning golden. It entered the Dutch language via Arabic and French, among other languages. The word jargon, used to denote light zircons, goes back to the same Persian word. Yellow zircon is called hyacinth. Zircon is a remarkable mineral found throughout the Earth's crust. It is primarily found in igneous rocks (as an early crystallization product) and in metamorphic rocks (in the form of new or recrystallized fragments). Dendritic zircons, formed by erosion of transported and deposited crystals, are found in sedimentary rocks. The average size of zircon is between 100 and 300 μm (in granite, for example), but occasionally specimens several centimeters in size are found (especially in pegmatites). The oldest minerals found on Earth to date are zircons from the Narryer Gneiss Terrane, Yilgarn Craton of Western Australia, with an age (crystallization period) of 4.404 Ga. There are deposits of heavy minerals in which zircon sometimes occurs in layers as the primary rock. These types of deposits are found in India, the United States, Australia, Sri Lanka, and South Africa. Zircon is one of the "nine gemstones" in the Thai Order of the Nine Gems. Zircon occurs in the sand fraction of Dutch Quaternary river sediments. In the heavy mineral analysis conducted in the Netherlands by the National Geological Survey during the second half of the twentieth century, the mineral is classified in the so-called stable group. Zircon is particularly abundant in Meuse sands.
The photo shows the Zircon Mine in Bahia.
