Although this banded type of rock is often called onyx or onyx marble and commercially traded as such, it is not true onyx. It is actually calcite, wh
Although this banded type of rock is often called onyx or onyx marble and commercially traded as such, it is not true onyx. It is actually calcite, whereas true onyx is chalcedony, a cryptocrystalline variety of quartz that has a much higher hardness and entirely different formula (SiO2).The multicolored banded calcite (CaCO3) here seen is formed by precipitation of dissolved calcium carbonate from ground or surface waters oversaturated with it. The coloring of the bands is caused by slight changes in the chemical composition of the water during is extensively cut and polished to make tiles, lamp foots, bowls, animal figures and other trinkets. Here it is seen in a polished slab of dimension 35 x 24 cm. True onyx is also worked into trinkets, but on a much more limited scale than the false calcite variety here displayed.
Size: 5173px × 3449px
Photo credit: © DIRK WIERSMA/SCIENCE PHOTO LIBRARY / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: banded, caco3, calcite, chalcedony, marble, onyx, rock, sio2, trinkets
