Chalcedony is a microcrystalline type of Quartz, the form of Quartz that is compact and formed of microscopic crystals. It occurs in many different forms, including stalactites & stalagmites. 
 
Fancy Chalcedony is also known as Merlinite (a marketing name for a white chalcedony containing dendrites), Chalcedonite, Ceracahtes.
 
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* Sizes, shapes and colors my vary due to being a natural stone, being hand-carved and/or difference in computer monitors.