Chalcedony: a microcrystalline fibrous variety of Quartz, occurring in the sub-varieties of Agate (yellow, brown, banded), Carnelian (orange, semitransparent brown), Chrysoprase (green due to the presence of Nichel), Chrome chalcedony (green due to the presence of Chrome), Eliotrope (green spotted red), Onyx (banded black and white), Plasm (opaque dark green due to the presence of Actinolite), Sardonic (brownish orange, semi opaque) as well as white, blue and light purple. Density 2.57-2.64 g/cm3; hardness Mohs 6,5; R.I.: 1.538-1.543.
