Buyer's Guide Zircon

Zircon
Thailand and Cambodia produces some of the world's most beautiful zircons. Originally the colors of zircons from these two sources are dark brown, orangy brown, yellow, yellow brown, red to dark reddish brown ( high zircons ). When heated these colors turn to blue and some begee colorless. Cut zircons can be very beautiful displaying a high dispersion and a high brilliancy with a diffused appearance due to its strong doubly refractive optical character. Zircon is brittle so care must be taken when setting the gem. The setting itself should protect the gem from exposing surfaces edges as much as possible for added protection. Sri Lanka and Burma also produces zircons. These two cources provide colors in green, dark green, brown,brown green ( low zircons ) yellow, yellow brown ( mediun zircons ) and an occasional red. The greens contain tiny metamict crystals with halo tnsion cracks around it. The prismatic crystals maybe radioactive elements such as U and Th. It has been reported in gemological literature that the radioactivity destroys the crystal lattice and if left long enough the crystal itself begees and transforms into a mixture of quartz and zirconium oxide of an amorphous nature. Zircon's identifying features are its spectrum lines at 6535 and 6590 which are usually distinctly visible. Zircons gees in small and large sizes of up to 100 carats. Clean ones are rare. Colorless varieties are used as a diamond substitute. Collectors strive to gather a sample piece from each source with varying colors. Some study the internal inclusions sith attention to shape, color, forms and placements of the embedded crystals within the gem.
Medium dark, pure blue stones have the highest per carat value, estimated by Sinkankas (Standard Catalog of Gem Values, 2nd. Ed), at $150-$300 in large sizes, followed by blue with a slight greenish cast at about $100/ct.