Depending on impurities present during formation, the agate will exhibit varied coloration as the impurities work their way into the crystal lattice. This deposition occurs molecule by molecule, forming tightly packed fibrous microcrystalline quartz crystals that line the contact walls of the cavity. It forms when a silica-rich, gelatin-like solution fills an open cavity within rock and begins to deposit crystals evenly along the walls. Some people insist to strictly use the term agate to describe translucent chalcedony with circular banding patterns, but this stricter definition is not in general use.Ī banded Laguna Agate from Ojo Laguna, Mexico Like chalcedony, it may form in a huge variety of colors and patterns. The term agate may generally be used to describe any form of chalcedony that is translucent (light will pass through it). Dependent on impurities present during formation, chalcedony can form in a wide variety of colors including red, yellow, green, blue, purple, grey, white and numerous color hues in between.Ĭhalcedony is quite hard, being a 7 on the Mohs Hardness Scale, which makes sense considering quartz is the benchmark mineral for a 7. ![]() When free from impurities, chalcedony is colorless and transparent. Both quartz and moganite have the same chemical formula SiO2 (silicon dioxide) but different crystal structures. Microcrystalline meaning the crystals are microscopic and cannot be observed by the naked eye. Agate is any type of chalcedony which is translucent, while jasper is any type of chalcedony which is opaque.Ĭhalcedony is any microcrystalline variety of silica composed of very fine intergrowths of quartz and moganite. ![]() Chalcedony is a broad term to describe a microcrystalline form of silica.
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