Formula: NaBSi2O5(OH)2
Phyllosilicate (sheet silicate), borosilicate
Specific gravity: 2.46 to 2.49
Hardness: 3½
Streak: White
Colour: White, colourless
Solubility: Readily soluble in hydrochloric acid
Common impurities: Al,Fe,Mg,H2O

Evaporite Deposits

Searlesite occurs in boron-bearing evaporite deposits, in sedimentary rocks rich in sodium and potassium, and in alkaline pegmatites (Dana).


The old Searles deep well at Searles Lake, San Bernardino county, California, USA, was the first locality where searlesite was found. It occurred in clay at a depth of 540 feet as spherulites to about one millimeter, intimately associated with tiny grains of calcite, quartz, feldspar, chlorite and hornblende (AM 35.1014-1020).

The Silver Peak Range, Esmeralda county, Nevada, USA was the second known locality for searlesite, which was found here as crystals to 3 mm, containing less than one percent of impurities and very close to the theoretical composition (AM 35.1014-1020).

At the Green River formation in Sweetwater county, Wyoming, USA, searlesite has been recorded in drill cores in oil shale with shortite and tiny crystals of pyrite. At the bottom of the shaft searlesite is found in association with trona (AM 35.1014-1020).

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