Chrysoberyl

[Wwoofa]

Hi,
This month's "Gem of the Month" is .... Chrysoberyl.

Feel free to add more info & pics. If anyone has any questions about Chrysoberyl then this is a good place to post them.

You might like to change your "Gem of the Month" votes now that this one has been covered.

General Information:
The name Chrysoberyl is derived from the Greek words chrysos and beryllos, meaning "a gold-white spar". Despite the similarity of their names, Chrysoberyl and Beryl are two completely different gemstones, although they both contain Beryllium. Chrysoberyl is the third-hardest common gemstone with a hardness of 8.5 on Moh's scale, between Sapphire (9) and Topaz (8 ).

An interesting feature of its crystals is "twinning". Twinned crystals have a hexagonal appearance but are the result of a triplet of twins with each "twin" oriented at 120° to its neighbours. If only two of the three possible twin orientations are present, a "V"-shaped twin results. See the pictures below for some good examples.

The three main varieties of Chrysoberyl are: ordinary yellow/green Chrysoberyl, Cymophane ("cat's eye") and Alexandrite.

Alexandrite is a strongly trichroic gem and will exhibit emerald green, red and orange/yellow colours depending on the viewing direction. However, its most distinctive property is that it also changes colour in artificial (tungsten/halogen) light compared to daylight. Fine-quality Alexandrite has a green to bluish-green colour in daylight changing to a red to purplish-red colour in incandescent light.

Cymophane is popularly known as "cat's eye". This variety exhibits chatoyancy or opalescence. When cut to produce a cabochon it forms a light-green gem with a silky band of light extending across the surface of the stone.

More info about Alexandrite can be found here ...
http://aussielapidaryforum.com/forum/index.php?topic=3476.0

Here are a few useful links that should cover all of the main information.

Wikipedia - http://en.wikipedia.org/wiki/Chrysoberyl
Mindat - http://www.mindat.org/min-1039.html
Gemdat - http://www.gemdat.org/gem-1039.html
Minerals - http://m.minerals.net/gemstone/chrysoberyl_gemstone.aspx

Fossicking Locations:
The main location for finding Chrysoberyl is Harding Springs, Harts Range in NT.

More info about this location and lots of great pics by Patrick can be found here ...
http://www.mindat.org/loc-209093.html

Info about fossicking in the NT can be found here ...
(Note that some of the embedded links don't work but if you use the menus at the top of the page they do work.)
http://www.nt.gov.au/d/fossicking/map-of-nt.cfm

PDF version of the info ...
http://www.nt.gov.au/d/fossicking/Content/useful-info/GuideToFossickingintheNT.pdf

Some beautiful examples of cut Chrysoberyl posted by kutter



Some beautiful examples of rough Chrysoberyl posted by PartickG

[gammyknee]

 
Like to hear some more on this

[gammyknee]

Very overcast and dull today so I tried to photograph some with and without light assistance.
The result...