Jasper is a varitey of microcrystalline quartz, but with impurities to result in a variety of colors.
Jasper comes in many varieties due to the different chemical impurities, as can also exhibit different ‘patterns’ in the stone due to the environment in which it formed. A number of these varieties have their own names which are purely trade names, not scientific. One of the most common is the red jasper, which is gets its red color from hematite. Autumn jasper often has colors of green, red, orange, brown, and white all mixed together and often speckled in appearance. Kambaba jasper is a green and black jasper that often has swirling patterns, and is sometimes mislabeled as rhyolite. Known as both Kiwi jasper and Sesame jasper, this stone has a spotted pattern of white, blue, and black. Another common jasper is Zebra jasper, which has bands of white and black.
There are many varities of jaspers known by specific trade names. Clockwise from the top is: Kiwi/Sesame jasper, Zebra jasper, Kambaba jasper, and Autumn jasper.
Two of the most sought after jaspers currently are the Ocean jaspers and Imperial jaspers. Ocean jasper, also called Orbicular jasper, forms when Rhyolite (an igneous rock) becomes silicified. In other words, the rock eventually is entirely replaced with silica (aka jasper). Rhyolite itself is silica rich, and as it cools sometimes the silica in the rhyolite can form spheres – hence the pattern commonly seen in Ocean jasper. Imperial jasper comes in shades of green, pink, brown, yellow, purple, cream – the two most sought after being the purple and green Imperial Jasper. It’s a beautiful stone, with rich colors often with subtle flowing patterns.
Jaspers provide a varitey of beautiful stones for jewelry work, such as this green Imperial Jasper.
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Chemical composition: SiO2 + impurities
Color: Many colors
Habit: Commonly massive
Fracture: Uneven and conchoidal
Specific Gravity: 2.65
Occurrence: Worldwide, though some varieties are only mined from specific locations (e.g. Ocean Jasper and Imperial Jasper)
A Guide to Rocks and Fossils by B. Busbey III, R. R. Coenraads, P. Willis, and D. Roots. Published 2002 by Fog City Press. ISBN: 1877019518
Rocks, Minerals, & Fossils of the World by C. Pellant and R. Phillips. Published 1990 by Little, Brown and Co. ISBN: 0316697966
Mindat – Jasper. http://www.mindat.org/min-2082.html
Mindat – Orbicular Jasper. http://www.mindat.org/min-27171.html
Wikipedia – Amazonite. http://en.wikipedia.org/wiki/Jasper