2 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.60. 



andorite-quartz intergrowths or andorite shells inclosing a large 

 amount of quartz. The prisms, which have ragged edges, reach an 

 extreme length of 1.5 cm. with a width of 4 mm. They lie dis- 

 seminated in the granular quartz like phenocrysts in a porphyry 

 and show no regularity of arrangement. The associated sphalerite, 

 which is dark brown with well developed cleavage, forms rounded 

 grains up to 1 mm. in diameter disseminated in the quartz between 

 the andorite prisms. These are apparently replacements of the 

 quartz and while grains of sphalerite occasionally have a core of 

 andorite the andorite never incloses sphalerite. The sphalerite shows 

 a purple-gTay color and metallic luster on polished surfaces. The 

 andorite has a brilliant metallic luster and light lead-gray color. 

 It is devoid of cleavage and has a conchoidal fracture when unaltered. 

 The hardness is about 2.5 and on unglazed porcelain the mineral 

 yields a soft dull black streak which when rubbed with a glass rod 

 becomes first shining and then decidedly brown. The mineral as- 

 sumes a yellowish tarnish upon exposure. Material was hand picked 

 for analysis, care being used to avoid, as far as possible, the material 

 showing the alteration described below. The analyzed sample con- 

 tained some quartz and also a little sphalerite, the latter mineral 

 being recognized as isotropic dark brown grains when the analyzed 

 powder was examined under the microscope. Insoluble quartz de- 

 ducted, the analysis yielded the following percentages : 



Analysis of andorite from Nevada. 



Lead (Pb) 23. 35 



Silver ( Ag) 12. 09 



Iron (Fe) 1. 55 



Zinc (Zn) 3. 56 



Antimony (Sb) 37. 64 



Sulphur (S) 22. 63 



Total 100. 82 



Of the above tabulated constituents zinc is certainly foreign and 

 present as sphalerite and it seems most reasonable to consider the 

 iron as also extraneous and associated with the zinc sulphide as an 

 impurity. These metals deducted, the analysis furnishes the follow- 

 ing ratios: 



Ratios of andorite from Nevada. 



Pd 0.1127 11.27 1.13x1 1.09x1 



Ag .1121 11.21 1.12x1 1.08x1 



Sb .3131 31.31 1.04x3 1.00x3 



S .7057 70.57 L 01 x 7 .97x7 



These ratios indicate closely the andorite formula: 

 PbAgSbjS^ or 2PbS.Ag2S.3SbjS3. 



