Precious Opal Pseudomorphs after Gaylussite found in Tecopa Dry Lake Sediments, Inyo County, CA

Robert Housley1, Marek Chorazewicz2, George R. Rossman1

1Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125-2500, U.S.A.
2124 Pineplank Lane, Simi Valley, CA, U.S.A.

Tiny precious opals are abundant in siliceous nodules from certain parts of the ancient Lake Tecopa sediments. The precise arrangement of silica balls that leads to the intense play of colors was determined for a single sample by (Ma and Rossman 2003).  More recently (Martin and Gaillou 2018) used isotopic measurements of oxygen and hydrogen to argue that these opals formed under ambient conditions. We have found searlesite blades in the same nodules in which the opal occur.

Tecopa Opal  Tecopa opal

Tecopa opals