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Roger Weller, geology instructor                                       

wellerr@cochise.edu
Quartz Family Gemstones-by Audrey LaClair
                            
                            Chrysoprase

Chyrsoprase is a variety of microscrystalline quarzt (chalcedony) and is the most valuable of that variety.  It is made up almost entirely of silicon dixiode.  Chyroprase is green in color because of traces of nickel in the quartz.  The green can range from pale green, to a apple green, and all the way to a deep rich green.  It is usually translucent, but can be opaque if it is of poor quality.  It's highest quality is when the quartz is a rich apple green and has no flaws, inclusions, or other imperfections.  It will fade in the sunlight.

photo by R.Weller

Chryspoprase is mostly found today in Australia, but can also be found in Brazil, California, and the Ural Mountains.  It is often referred to as Australian Jade because of it's rich green color.

"Chrysoprase occurs within the deep weathering profile that results from lateritiseration of nickeliferous serpentinites or other ultrabasic rocks" (http://www.nrm.qld.gov.au/mines/fossicking/chrysoprase.html).

"Mine workings consist of large open-cuts. Heavy earth-moving machinery is used to excavate benches within these. The barren iron-rich cap of the deep weathering profile, which may be up to 40 m thick, is removed by bulldozer.  The underlying saprolite (soft, earthy, clay-rich) zone, in which the chrysoprase veins and nodules occur, is progressively stripped and the freshly exposed floor is checked for signs of chrysoprase after each bulldozer pass.  When chrysoprase is exposed, the veins are removed by backhoe or excavator, and the chrysoprase is collected by hand. It is later cleaned using a high-pressure water spray; separated by wet trommelling; sorted for quality; and finally packed in drums for dispatch to market" (http://www.nrm.qld.gov.au/mines/fossicking/chrysoprase.html).
 

photo by R.Weller

Physical Properties

·        Colour: pale green, yellowish green, apple green, deep green

·        Diaphaneity: translucent to opaque

·        Lustre: vitreous to resinous

·        Hardness (Mohs scale): 6–7

·        Specific gravity: 2.58–2.64

·        Refractive index: 1.53-1.54

·        Birefringence: form birefringence 0.004

·        Chelsea filter reaction: green

·        Ultra-violet fluorescence: none

Source from (http://www.nrm.qld.gov.au/mines/fossicking/chrysoprase.html).

References

http://www.australianjade.com.au/myframes1.html
http://www.nrm.qld.gov.au/mines/fossicking/chrysoprase.html
http://www.jewelrymall.com/stones/chrysoprase.html