The zircon, hyacinth, jacinth, or jargoon belong to the tetragonal system of crystallization. The cleavage is imperfect, fracture conchoidal, and specific gravity 4.4 to 4.7, the stone being much heavier than any other gems. Its hardness is 7.5 and lustre vitreous to adamantine, and refraction double to a high degree.

The zircon is phosphorescent when heated; before the blow-pipe it is infusible, but loses its color; and with borax it melts into a transparent glass. Sulphuric acid affects this gem after long maceration.

The composition of the zircon is: zirconia, 66.3; silica, 33.7; with a trace of peroxide of iron.

Under the microscope, the texture of these gems presents a watery appearance, called by the French ratinÉ, and which looks like a liqueur poured into water. This is a strong distinguishing point in the zircon.

The zircon, hyacinth, jargoon, and jacinth are the same gems but of different colors.

The brown, violet, and green colors are known as zircons, the red as hyacinth, the yellow as jacinth, and the grayish-white and white as jargoons.

The jargoon has often been palmed off as a diamond because of its transparent color and adamantine lustre.

The zircon is found in Ceylon, Germany, France, Bohemia, America, and in fact in nearly all parts of the earth, as many as 120 localities having been noted where specimens of the mineral have been discovered.

The zircon can be distinguished from the garnet by its peculiar diamond-like brilliancy and its specific gravity.