Epigenetic common opal from the Hawkesbury Sandstone Formation of the Sydney Basin
Abstract
An unusual occurrence of epigenetic common opal, apparently derived from the normal ground-waters of the Hawkesbury sandstone formation of the Sydney Basin, is described. The opal forms simple and botryoidal incrustations, simple and coralloidal stalactitic structures and also is deposited on stalactites of lamellar limonite. Refractive index values vary widely and haphazardly between 1.414 and 1.443.
