2.7" Polished Sulemani Agate Bowl
This is a 2.7" wide polished Sulemani agate bowl from India. Sulemani agate is the trade name for a dark brown-black chalcedony with white and colorless banding. While some consider it to be onyx (parallel banding), for the sake of convenience, we refer to it as agate. Even the darkest agate portions of this bowl are slightly translucent.
Agate is a variety of microcrystalline quartz that displays translucence and in some cases banding. Agate primarily forms when silica-rich fluids fill pockets within rock and/or fossils, resulting in deposition of the silica along the walls of the rock. This process can result in banding patterns as the composition and impurities of the fluids change over time. These banding patterns can either form as flat layers or rounded layers, depending on the surfaces available for deposition.
Silicon Dioxide, also known as SiO2 or Quartz, is the second most abundant mineral in the Earth's crust. Quartz crystals generally grow in silica-rich, hot watery solutions called hydrothermal environments, at temperatures between 100°C and 450°C, and usually under very high pressure. Quartz veins are formed when open fissures are filled with hot water during the closing stages of mountains forming, and can be hundreds of millions of years old.