“Genesis And Classification Of Agates And Jaspers: A New Theory” Book Review
|Is a Variety of||Chalcedony|
|Varieties||Dallasite, Orbicular Jasper, Plasma|
|Luster||Waxy to dull.|
|Luminescence||Varies widely in cryptocrystalline quartz due to traces of impurities.|
|Enhancements||Dyeing: common, stable. Detected by appearance, spectrum, or Chelsea filter. Heating changes color, common, stable, undetectable.|
|Typical Treatments||Dyeing, Heat Treatment|
|Absorption Spectrum||Dyed green gems show weak lines at 6450 and 6700 nm. Dyed blue gems at 6270, 6660, and 6900. Others not diagnostic.|
o = 1.540; e = 1.553. Uniaxial (+).
|Optic Sign||Uniaxial +|
Jasper is an opaque, solid or patterned variety of cryptocrystalline quartz which consists of very tiny quartz crystals colored by various mineral impurities. The names of various jaspers can come from their color: bloodstone, green, lemon; from their pattern: orbicular, poppy, leopardskin, landscape, Picasso; or from a place name: Morrisonite, Mookite. All types take an excellent polish, are trouble free to care for, and hardy enough for all jewelry uses. These stones are usually cabbed, sometimes carved, and seldom faceted. Jewelry use of jaspers goes back into the early history of civilization. Various forms of this material are also frequently made into decorative objects, such as ashtrays or bookends. Jaspers are found all over the world, with certain colors or patterns unique to particular locales. Most bloodstone comes from India, all Mookaite from Australia.
Some of the most treasured gems are those that show a picture that appears to be taken from nature. Oregon’s Biggs Jasper is now the most common source. Bruneau Jasper, from Bruneau Canyon, Idaho, used to be the preferred material. Gems from this locality frequently had blue “skies” which the Oregon material lacks. Unfortunately, a dam has submerged the mining site and the material is now quite rare.
Jaspers, in general, are very common; hence most of the value in a given piece relates to the saturation of its color, the beauty of its pattern or the artistry with which it is fashioned. Some types such as Imperial Jasper and Madagascar Jasper do command premium prices since they are relatively rare. In rock shops, pieces of commercial quality cut in simple shapes might be had for $5 or less. Fine material, cut in designer forms, generally ranges between $2 and $5 per carat.
Agate prices are generally quite modest – most of the price one pays is for the fashioning of the material, rather than the material itself. In the case of the agates pictured above, those with particularly distinctive or landscape like patterns, or those of especially large size, premiums may be paid. Wholesale values of commercial grade standard cabs range from $.50 – $20 each, depending on size. Custom cutting or pieces from collectible locations would be substantially more expensive. Especially fine patterns are cited as bringing up to $200 per piece.