Gaylussite and Hanksite froin California. 133 



For red, Des Cloizeaux measured 51° 50' at 21*5° C. and 

 53° 32' at 71-5^ a variation of V^^\ 



Hanlcsite. 



This mineral was first identified in 1885 by Mr. W. E. Hid- 

 den,"^ who observed some crystals with hexao^onal habit marked 

 thenardite, in the mineral exhibit from California, at the 

 World's Industrial and Cotton Centennial Exposition, held in 

 Xew Orleans. Upon examination these crystals proved to be 

 a new mineral, to which the name, hanksite^ was given in 

 honor of Mr. H. G. Hanks, formerly State Mineralogist of 

 California. 



The mineral occurs at Borax Lake in many places. Accord- 

 ing to information received from Mr. Xorthup, short crystals 

 with prominent basal planes are. found near the surface, either 

 attached to the under side of the crust, already referred to on 

 page 121 of this article, or in the mud directly beneath this. 

 The habit of these crystals is illustrated by figures in the 

 articles by Hidden and Hanks. f Beneath the crust, for a dis- 

 tance of about 50 feet, hanksite crystals are rare, but at this 

 depth a stratum of mud was encountered, containing a few 

 crystals with a habit somewhat resembling quartz, shown in 

 fig. 10. The crystals were etched to such an extent that they 

 could not be measured with the reflection goniometer, but by 

 means of the contact goniometer the forms were identified as 

 the prism m^ 1010, and the unit pyramid o, 1011. 



Optical jproperties. — As the indices of refraction of hanksite 

 had not been determined, a basal section was prepared from a 

 tabular crystal, and by means of total reflection the following 

 values were obtained : 



For yellow, Xa, co=l-4807. €=1-46U. 



The section showed a normal uniaxial interference figure 

 and a strong negative double refraction. 



Chemical comjyosition, — Our knowledge concerning the 

 chemical composition of hanksite is confined to two analyses. 

 One by Mackintosh, quoted by Hidden, :J from which the for- 

 mula, iXa^SO^ -f Xa^COg -h I .NaCl was derived. Sodium 

 chloride, however, was regarded as non-essential and 4]S^a2SO^ -1- 

 Xa^COg was suggested as the probable formula. It should be 

 pointed out, however, that a mistake in the calculation of the 

 analysis was made, for while the ratio of Xa^SO^: XajCO, : 

 XaCl is given as 3-95 : 1 : -16 or 4 : 1 :-J, it should have been 



* This Journal, xxx, p. 33. 18S5. f Ibid., xxxvii, p. 66, 1889. 



:j:Ibid., XXX, p. 134, 1885. 



