Gaylussite and HanJcsite from California. 125 



from Mr. Xorthup, it has been found in only one boring, 

 known as the "Xew Well," and was probably formed in a 

 stratum of clay, about 450 feet below the surface. With two 

 exceptions, north upite has been observed only in detached 

 crystals, Mr. Poote having in his possession a single specimen 

 showing two octahedrons of northupite attached to a crystal of 

 the new mineral, pirssonite, to be described beyond, and a 

 similar specimen being in the Brush collection. 



Physical pro])erties. — The crystallization is isometric, the 

 octahedron being the only form observed. The crystals vary 

 in size from less than a millimeter to rarely a centimeter in 

 diameter. There is no apparent cleavage, but the crystals, 

 which are extremely brittle, break with a distinct conchoidal 

 fracture. The luster on fractured surfaces is decidedly vitre- 

 ous. The hardness is between 3*5 and 4, The specific gravity 

 was obtained by floating the crystals in methylene iodide 

 diluted with methyl iodide and was found to be 2'3S0. The 

 pure material is colorless, but owing to impurities the color of 

 the crystals, as stated by Foote, varies from dirty white, pale 

 yellow and greenish gray to dark brown. The impurities are 

 probably clay or organic matter and Foote has called attention 

 to their arrangement in directions parallel to the axial planes 

 of the isometric system. Xo decomposition on exposure to 

 the air has been observed. 



Optical properties. — Fragments of the mineral, when exam- 

 ined in polarized light, were found to be isotropic. By means 

 of a prism of 79' 35' the following indices of refraction were 

 determined : 



n,— 1-5117 Li. n,^— 1-5144 Xa. n,,. — l-ol80 Tl. 



Chemical composition. — A qualitative examination showed 

 the presence of carbonic acid, chlorine, sodium, magnesium 

 and minute traces of sulphuric acid and water. Potassium 

 was very carefully tested for, but not even a trace of it could 

 be detected. 



The results of the analyses are as follows : 



I. II. Average. Ratio. 



CO3 --- 35-21 35-02 35-12 -798 2-01 



CI 14-10 14-10 -397 1-00 



SO3 -08 -08 -08 



MgO 15-96 16-20 16-08 '402 1-01 



Xa,0 36-99 36-99 -597 1-50 



H,0 -72 -72 -040 



IdsoI -25 -19 -22 



103-31 

 equivalent to CI, 3-16 



100-15 



