Stone of the Week - Jasper

Jasper is a type of Chalcedony, which in turn is a cryptocrystalline variety of quartz (cryptocrystalline = crystals so small you can’t see them). Hence it also has the chemical formula SiO2, but with impurities that result in the myriad of colors. One distinction between jasper and other forms of chalcedony is that it is usually opaque; whereas other forms of chalcedony such as agate will exhibit some translucence. The name jasper means “spotted stone", and comes from the Anglo-French word ‘jaspre’ that is derived from the Greek word ‘iaspis’.

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.

If there's a stone you would like to know more about - drop me a line! Have a mystery stone? Feel free to post a comment about it, including a link to a picture, and it could be featured on this blog!


Jasper Facts:
Chemical composition: SiO2 + impurities
Color: Many colors
Habit: Commonly massive
Fracture: Uneven and conchoidal
Cleavage: None
Luster: Vitreous
Hardness: 7
Specific Gravity: 2.65
Streak: White
Occurrence: Worldwide, though some varieties are only mined from specific locations (e.g. Ocean Jasper and Imperial Jasper)


References
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