Grey Agate

chalcedony (kal-SED-uh-nee) is microcrystalline or cryptocrystalline quartz; hexagonal (trigonal) crystal system; chemical composition SiO2
semitransparent to opaque
milky chalcedony – semi transparent to translucent, nearly colorless or white
natural material no any treatment, we should call this material “chalcedony”, while always use grey agate to call it in the gemstone business
agate is use for the banded material, while there is no stripes in it

Identification

Optic Character: AGG
Refractive Index: 1.535-1.539; 1.53 or 1.54 spot reading
Birefringence: usually not detectable, but may show .004
Pleochroism: none
Ultraviolet Fluorescence: generally inert (LW and SW); some may fluoresce a yellowish green (LW and SW)
Absorption Spectra: dyed green – vague lines around 645 and 670 nm
Specific Gravity: 2.60 (+.10,-.05)
Polish Luster: greasy to vitreous
Fracture: conchoidal; sometimes granular
Luster: dull to waxy
Cleavage: none
Identifying Characteristics: dyed green and dyed blue appear red or pinkish through Chelsea filter
Crystal Habit: aggregate, often in botryoidal forms
Hardness: 6 ½ to 7
Toughness: good

Gem Reference Guide, Published by GIA. ISBN 0-87311-019-6

Gemstones of the World, Published by Sterling Publishing Co., Inc NY, ISBN 1-4027-4016-6

Encyclopedia of GEMSTONE, Published by ISHINSHA CO., LTD. ISBN 978-986-251-831-1