32 



University of California. 



(Vol. 3. 



measurable crystals afforded an opportunity to make a very 

 complete crystallographic study of this borate. The suite of 

 crystals selected for measurement included probably all of the 

 habits, and possibly all of the forms, possessed by the mineral. 



The measurements were made with the two-circle ( Zivei- 

 kreisige) goniometer, designed by Goldschmidt. Since the 

 method of measurement with this instrument and the gno- 

 monic projection are as yet not generally understood by 

 American readers, a detailed statement of the work follows 

 the description of the crystals, which will make clear the 

 steps used in the calculation and projection of the forms. 



Colemanite was first discovered in Death Valley, Inyo 

 County, California, in 1882, and in the following year the 

 more extensive deposits were found in the Calico District, 

 about five miles from Daggett, San Bernardino County. Most 

 of the fine geodal specimens are from the Calico District and 

 it is presumed that the crystals described here are from this 

 locality, as the labels indicate. 



The crystal forms of colemanite were first described by 

 Jackson.* His description of the crystals was quite complete 

 and forms the basis of what is at present known regarding 

 their forms. Some of his crystals were from the Death Valley 

 deposits, but the majority came from the Calico District. 



Others who have measured the crystals are: Hiortdahl,t 

 who published a short description of the forms and optical 

 properties, with a chemical analysis of a few crystals from 

 Death Valley; Bodewig and vom Kath,+ who likewise described 

 some of the Death Valley crystals, and also gave an account 

 of the origin of the deposits, and Arzruni,§ who described one 

 crystal . 



The crystals commonly line geodal- shaped cavities and 

 some are quite large, one in the collection having a width of 

 ten centimeters. They are colorless transparent, to white, 

 although a few are stained yellowish by iron. Most of them 



*A. W. Jackson. Bull, of Cal. Acad. Sciences, 1885, No. 2, 2-30, and 1886, No. 



4. 358-305. 



tTh. Hiortdahl. Zeitschrift fur Krystallographie, 1885. 10, 25-31. 

 JC. Bodewig und G. vom Rath. Idem, 179-186. 

 §A. Arzruni. Idem, 272-276. 



