Topic summary
Lithophysae
Extracted from the Wikipedia article Lithophysa.
Lithophysae are one of the many forms of silica (SiO2), as quartz, agate, opal, chalcedony, etc. They can have an average diameter 5–20 centimetres (2.0–7.9 in), but can be much larger (for example, 300–370 centimetres (10–12 ft) at Silver Cliff in Colorado). Lithophysae are also related to the spherulites found in obsidians on the Italian island of Lipari, in Yellowstone National Park, and other places.