Appearance:
• 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
Birthstone Designation(s):
• Chalcedony – 8:00 pm
Stone information is reference from:
• 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