In addition to being reddish brown, natural zircon may vary from almost colorless to yellow, red, orange, and brown or from yellow-green to dark green and, occasionally, blue. The most important producing areas of gem zircon are in a region of Indochina that comprises parts of Thailand, Viet Nam, and Laos. Additional gem zircon, like so many of the other gem species, is recovered from near Moguk in Upper Burma and from the gem gravels of Ceylon. There is no synthetic zircon on the market, but a bright blue synthetic spinel is sometimes used to simulate zircon successfully. PERIDOT The relative rarity of peridot and the ease with which it can be simulated in glass, whose luster it approximates, probably account for the low popular demand for this gemstone. Although peridot has little brilliance and no fire, its unusual color and glassy luster produce a unique effect that serves to make it attractive. The color of peridot is an unusual bottle green that shades, in some stones, toward yellow-green and, more rarely, toward brown. In 1952 it was discovered that almost all of the brown gems believed to have been peridot in various gem collections were actually of an entirely unrelated species, which since has been named sinhalite. Brown peridot still remains rare and is somewhat of a collector’s item. [Illustration: To exhibit its unique color to best advantage, peridot usually is cut so as to have a relatively large table, as shown in these examples. The largest gem, weighing 310 carats, is from the Egyptian island of Zebirget in the Red Sea and is the largest cut peridot known. The other two, weighing 287 carats and 109 carats, are from Burma. (Three-fifths actual size.)] The green of peridot, which is quite different from the green of other gemstones, is due to some iron included in its composition. It is suspected that a trace of nickel contributes to the liveliness of the color. [Illustration: This photo shows the color of peridot projected onto the background. The larger gem is the 310-carat stone shown in the prior illustration. The stone on the right weighs 109 carats and is from Burma; the other peridot weighs 46 carats and is from Egypt. (Almost actual size.)] Peridot has a hardness of only 6½ and a rather strong tendency to cleave, and these characteristics reduce its value for use in jewelry exposed to rough wear. It is better used in pins, earrings, and pendants than in rings. Peridot is a gem name for the common mineral olivine, a magnesium silicate. Olivine is fund in numerous places, and small gemmy pieces are found in many localities. Many of the largest and best gems of peridot have come from mines on the Egyptian island of Zebirget (Island of St. John) in the Red Sea, but most gem peridot now comes from Burma. Great numbers of small stones have been cut from olivine found in Arizona gravels.