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Volume 9, pages 11-13, 1924


     W. F. FOSHAG,1 United Stales National Museum

    In the field and in the literature frequent mention is made of the occurrence of priceite in California. In the course of an investigation of the borax deposits of the Mohave Desert Region by the writer all the reported localities were visited. Invariably the priceite proved to be the calcium silicoborate, howlite. At the mines the howlite is generally referred to as pandermite (= priceite). True priceite, not hitherto reported, was found during this investigation at a small prospect in the Furnace Creek Wash in Inyo County, about two miles below the mill of the Pacific Coast Borax Company.

     The priceite occurs as nodules and irregular masses embedded sporadically in a soft greenish gray shale. Near the surface the mineral is in soft chalky masses associated with colemanite and gypsum. With depth, the priceite becomes harder and more compact. The purest material is very compact and tough and breaks with a decided conchoidal fracture. The surface specimens resemble the priceite from Oregon while the more compact material is entirely similar to the mineral from Panderma. The color is pure white. Its hardness is 3–3.5. Sp. Gr. 2.43.

     The compact mineral is crystalline to cryptocrystalline. The softer material under the microscope is seen to be made up of shreds and small platy grains with occasional rhombic outline. These grains have a weak birefringence, are biaxial with positive optical character and a medium optic axial angle. The indices determined by the immersion method are:

     α=1.571, β=1.590, γ=1.593.

     For analysis the compact, pure white material was selected. Although very fine grained the material appeared homogeneous under the microscope. The results of the analysis together with the calculated ratios is given below:


SiO2 0.58 .575 5
CaO 32.20
Al2O3 0.20
B2O3 49.03 .700 6
H2O(-) 0.38 .990 9
H2O(+) 17.86


     The ratios therefore correspond to the formula usually given for priceite, 5CaO.6B2O3.9H2O. Van't Hoff, however assigned the formula 4CaO.5B2O3.7H2O to the mineral, artificially prepared. In the following table the three best analyses are compared with the theoretical compositions of the two ratios given.


  4:5:7 5:6:9 Foshag Van't Hoff Kraut
CaO 32.7 32.5 32.2 31.4 32.3
B2O3 51.0 48.7 49.0 48.9 49.9
H2O 16.3 18.8 17.9 18.9 18.2

     The agreement is sufficiently close to accept the ratios of priceite as 5CaO.6B2O3.9H2O.

     The minerals associated with the priceite are colemanite and gypsum. Both of these minerals were observed only in the specimens from the surface. The colemanite forms small crystals coating the sides of the cavities or attached to loose masses of the priceite in the cavities. In some places the priceite gives way to vugs lined with small and brilliant colemanite crystals. The relations indicate clearly that the colemanite is the result of the surface alteration of the priceite. The gypsum is decidedly later than the colemanite as well as the priceite. It forms seams in the shale and fills cavities occupied by the colemanite.

     Van't Hoff synthesized priceite by the action of sodium and potassium chloride solutions upon ulexite at a boiling temperature. The Furnace Creek mineral, however, shows no evidence of having been derived from any preexisting mineral, but was probably deposited as priceite within the shales. In a recent paper by G. Linck,2 the priceite of Panderma was thought to be a direct precipitation from the boraciferous waters of lagoons, the precipitate being first amorphous but crystallizing upon standing. The general occurrence and the metacolloidal character of the California mineral would seem to bear out such a hypothesis. The mineral is of very local occurrence, however, and probably formed under conditions somewhat different from those that determined the formation of the large beds of ulexite and colemanite of this region.


     1 Published by permission of the Secretary of the Smithsonian Institution.   

     2 Centralblatt, Min. Geol., p. 193, 1923.

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