Zircon

"The oldest known rock in the world is generally believed to be a zircon from Canada estimated at nearly 4 billion years old." -- Gems: A Lively Guide for the Casual Collector by Daniel J. Dennis.

Zircon is a very interesting mineral -- non-gem zircon rock is mined to extract the zirconium metal used in various alloys. Pure zircon crystals are colorless and used to be sold as a diamond substitute, although they are doubly refracting and hence even more sparkly than real diamond (they're also much more brittle). Colorless zircon can also be made from the more common brown stones by heat treatment; blue and golden-yellow stones are also made this way. The most common non-treated zircons are honey-brown and called "hyacinth."

A few varieties (called "low zircon") are actually very slightly radioactive -- not enough to hurt their wearer, but enough that their crystal structure breaks down and the stone loses its luster. The jewelry trade avoids these as much as possible.

Zircon is also an IRC client, written by Lindsay Marshall.

It was the first GUI IRC client I've ever used on Linux. (I have used some graphical IRC clients in Windows, but those sucked. And no, I haven't used mIRC at all =)

The toolkit it uses is Tk, and it was written in Tcl. According to the hype, it supports all ircII features and more.

I don't remember much about it, but I remember one curious feature: Plain <ENTER> sent a line, while <Shift+ENTER> sent the line as an action (this is done in other clients with /me).

Home page as of writing: http://catless.ncl.ac.uk/Programs/Zircon/

Chemical Composition: Zr(SiO₄)
Mohs' Hardness: 6.5-7.5
Specific Gravity: 3.90 - 4.71
Refractive Index: 1.777-1.987
Double Refraction: +0.059 (none in Green Zircons however)
Dispersion: 0.039

Zircon varies greatly in both color and transparency. Most natural zircons are a brownish mixture of red and yellow. However, clear, yellow, grey, blue, greenish, and darker zircons have been found. The red/yellow zircons are more commonly known as hyacinth. When treated with a heat of 1472-1832°F (800-1000°C) zircon looses it's color and becomes clear or blue. This is done rather often, especially in Asia, and most zircons for sale at a jewelers will be blue or clear, but sometimes the reddish-orange of Hyacinth too. Green zircons are extremely rare, and therefor more expensive. Zircon, while a hard gem, does not always make the best jewelry as it can easily chip and flake. Most zircons for sale are transparent or slightly cloudy.

Hyacinth is often mistaken for another gem, hessonite, and sometimes even colored glass. The easiest way to tell hessonite and hyacinth apart is by their refractiveness. Hessonite is only singly refractive whereas hyacinth is doubly refractive. Glass differs in lustre, specific gravity and hardness, and can be discovered by any tests for one of those properties.

Zircon is found inside igneous and some metamorphic rocks as small crystals or grains. Rarely will more than 1% of the entire mass of a rock consist of zircon. Zircon crystals are tetragonal in shape. Geographically, zircon can be found in Cambodia, Burma, Thailand, Sri Lanka (specifically Myanmar), Australia, The Malagasay republic, Tanzania, Vietnam, France, Maine and South Carolina.

Zircon is usually defined into two different categories, high zircon and low zircon. High zircon is transparent or translucent and has higher marks in both refractive indeces as well as a higher specific gravity. Low zircon has lower numbers in those properties. The large discrepency in values is due to the amount of radioactive elements, such as uranium or thorium, in the stone. However, the amount of radioactivity in the stone will not harm the wearer of a piece of zircon jewelry. Zircon is also in no way associated with Cubic Zirconia, the synthetically made diamond.

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Sources:
Precious Stones, by Dr. Max Bauer. Charles E. Tuttle Company: Rutland Vermont and Tokyo, Japan, 1969
Gemstones of the World, by Walter Schumann. Sterling Publishing Co., New York, 1979
http://webmineral.com/data/Zircon.shtml
http://www.mindat.org/show.php?name=Zircon

Zir"con (?), n. [F., the same word as jargon. See Jargon a variety of zircon.] Min.

A mineral occurring in tetragonal crystals, usually of a brown or gray color. It consists of silica and zirconia. A red variety, used as a gem, is called hyacinth. Colorless, pale-yellow or smoky-brown varieties from Ceylon are called jargon.

<-- 2. an imitation gemstone made of cubic zirconia. -->

Zircon syenite, a coarse-grained syenite containing zircon crystals and often also elaeolite. It is largely developed in Southern Norway.

 

© Webster 1913.