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Gemstone Crystal System Density Hardness Refractive index Treatments
Agates microcrystalline 2.66 6.5-7.0 1.544-1.553 dying

 

 

 

dyed agates
All the examples of agate, onyx and chalcedony above have been dyed!

 Dying Chalcedony, Agate and Onyx
first involves boiling the stone in a
strong bicarbonate solution, then soaking the stone in a
chemical solution.

Red: iron nitrate solution
Green: chromic acid or nickel nitrate
Brown: sugar solution followed by heat.
Blue: red or yellow prussiate of potassium followed by
soaking in iron sulphate solution
Black: sugar solution followed by suphuric acid.

Agate has been mined along the Nahe River Valley in Germany since the 1400's. The Nahe River was used to power the grinding wheels for stone cutting in Idar-Oberstein. When the agate deposits were depleted along the Nahe River in the 1800's, the gem cutters in Idar-Oberstein started importing material from Brazil. Exploration led to discoveries of amethyst, citrine, tourmaline, topaz, and other gemstones.
Idar-Oberstein is still known for the finest agate carving in the world, today Idar imports a huge range of other gem materials from around the world for cutting and carving in Germany and Asia. Cameo master carvers and modern lapidary artists flourish along with rough dealers who scour the world for the latest gem discoveries for export.