Natural Onyx — Rough

Onyx is a variety of chalcedony (SiO₂) with a microcrystalline structure, formed by alternating and parallel layers of black and white chalcedony. Its formation occurs in cavities in igneous and sedimentary rocks, where silica-rich hydrothermal solutions deposit successive layers of minerals over time, creating the species' characteristic banded structure. The black color — predominant in the most commercialized variety — results from the presence of carbon or manganese and iron oxides incorporated during the deposition of the silica layers. Much of the black onyx available on the market goes through a dyeing process with carbon salts, a consolidated practice widely used in the mineral production chain. Hardness: 6.5 to 7 on the Mohs scale. Density: 2.55 to 2.70 g/cm³. Crystalline system: trigonal (microcrystalline). Available variations, approximate data: 1 to 3 cm — Approx. 0.010 kg — 250 pcs per kg 3 to 6 cm — 0.030 to 0.150 kg — 30 pieces per kg 6 to 15 cm — 0.150 to 0.800 kg — 2 to 3 pieces per kg