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University of California Publications. [Geology 



NEOCOLEMANITE 



Occurrence. — A deposit of calcium borate occurs at the head 

 of a valley about five miles northwest of Lang, a station of the 

 Southern Pacific railway in Los Angeles County, which is owned 

 and now mined by the Sterling Borax Company of Los Angeles. 

 The borate is known as colemanite and in its chemical com- 

 position and general physical properties it agrees witfh the 

 colemanite from the Death Valley and Calico districts, but in 

 its optical and crystallographical properties it is somewhat 

 different, so the name neocolemanite is proposed to distinguish 

 it as a variety of colemanite. 



The mineral occurs as a stratified deposit, the strata alter- 

 nating with layers of black carbonaceous shales, and the main 

 seam of the solid mineral is from six to ten feet thick. A 

 northern uplift has tilted the deposit so that the bands of 

 mineral and shale stand almost vertical, the dip being about 80° 

 south. The shales underlying the mineral layers are of consider- 

 able thickness, while above the deposit are heavy bedded sand- 

 stones. These sandstones show efflorescences of white alkali salts 

 along their seams and bedding planes. 



The shafts and mining operations are carried down on the 

 main seam of the mineral and they are now down 250 feet with 

 no apparent change in the dip or width of the bed. The lateral 

 extent of the deposit is not yet determined, but it is evident that 

 an extensive deposit of the pure borate exists. A narrow-gauge 

 road connects the mine with Lang and all of the material is 

 hauled to this station and shipped to Chicago and San Francisco. 

 The poorer grade is separated from the gangue and impurities by 

 calcination at the mine and then shipped in sacks. 



Origin of the deposit. — The bedded character of the deposit 

 is evidence that the mineral crystallized from an evaporating 

 solution and that precipitations of both the borate and some of 

 the silt which formed the shales took place. The solution filled 

 a closed basin as a lake or marsh, probably similar to the alkali 

 marshes of the desert regions. It is generally characteristic of 

 such deposits that salts of various kinds, often in alternating 



