Chalcedony is a variety of Quartz, defined as cryptocrystalline, meaning individual crystals are too small to see, even with a microscope. Though it is not technically its own mineral species, the name has been used and implied for ages, with almost all mineral reference guides, in print and online, and collectors, referencing Chalcedony independently from Quartz. It is translucent and exhibits a waxy luster. In its pure form it is white, light gray or dull blue. However, due to myriad of potential mineral inclusions, the color spectrum now expands to literally any color you can imagine. And multicolored! There are numerous varieties of Chalcedony, including Agate (with its own category), Carnelian, Chrysoprase, Jasper, Onyx, Sardonyx and Tiger’s Eye. There are simply too many varieties (and their locations) to list; one site lists 72 varieties.

When it comes to crystal systems, in essence, there is none; being cryptocrystalline, it does not occur in visible crystals. Chalcedony is, however, quite varied in its formation habits, including botryoidal, mammilary, stalactitic, massive, nodular, banded, in geodes, and pseudomorphs after organic material (petrified wood, coral agate).