Precious Opal Pseudomorphs after Gaylussite: From Tecopa Dry Lake Sediments, Inyo County, CA

Abstract

Tiny precious opals, usually not more than one quarter inch in diameter, are abundant in siliceous nodules from certain parts of the ancient Lake Tecopa sediments. This occurrence must have been known to some local collectors since at least as early as 1885. At that time the Harmony Borax Works owned by Coleman and Company operated in Death Valley during the cooler parts of the year (Tarman and Jessey 2004). They refined borax from cotton ball ulexite/probertite nodules, collected off the dry lake surface by a simple process. They simply dissolved the nodules in boiling water and let the borax crystallize out on cooling. During the summer the water would not cool enough to crystallize borax in Death Valley, so they moved their operations to Tecopa Dry Lake where it was sufficiently cooler to continue production.