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mineral data
Mineral Name: zircon
Gem Names: zircon
Chemistry: ZrSiO4
Class: silicates - neosilicate
Crystal Sys: tetragonal
Hardness: 7.5 Specific Gravity: 4.6 - 4.7
Fracture: conchoidal Refractive Index: 1.92 - 2.02
Dispersion: 0.039 (high)
Misc Prop: Zircon had a high refractive index, great dispersion, and is doubly refractive. It produces one of the brightest stones there is next to diamond. Clear zircon (white) has been used as a diamond substitute. Do not confuse the mineral zircon with the similarly named zirconia (CZ or cubic zirconia). The CZ is a nearly pure ZrO2 and not a silicate like zircon. They are not related in any way beyond both materials containing some Zr.

There are two categories of zircon, "high zircon" and "low zircon". The high zircon has better transparency and more consistent index of refraction and specific gravity. The "low zircon" has traces of uranium or thorium in the structure, and the radio active decay of these trace elements destabilizes the crystal structure making their physical properties less reliable. Low zircon is a bit of a collectors item but usually not used in jewelry. (The radiation is usually low enough that they do not cause physical harm.)

The most common zircon is the brown to red-orange zircon and may be quite pleasing but the most popular color today is the blue zircon. Funny, the blue zircon is usually created by heat treating some brown zircons. Zircons are commonly heat treated to improve color, or the clarify of the stone. The blue is sky blue and they are similar in color to sky blue topaz, but easily identified due to their double refraction, and much greater color dispersion.

The orange to light yellow-brown stones are sometimes called "honey zircon" and may be quite attractive. They are often the least expensive, although many are used to create blue or clear zircons through the heat treating process. Thus many honey colored zircons never make it to market as honey colored stones.

There is a red zircon which is highly prized if it is not too dark. In most gemstones, dark red is usually desirable, but in the case of zircons dark red stones lose some of the color play associated with high dispersion and index of refraction. Some of the red to red-orange stones are called "hyacinth".

The rarest color is green and is a collectors stone although not a jewelers item to any great extent.

Color: In gemstones, color, is often the key to naming or describing the particular variety. Hence look for this information below in the various descriptions. Color, opacity, and homogeneity often determine the placement of value on any given stone, and are all optical properties of the particular stone.
Specific Data:
a large round and 4 small matching stones
dark honey colored zircon better than average cut - triangular cut
yellow - tan colored zircons one round, one triangular cut
a small lemon yellow round with average color return