1887.] 4:'J [Genth. 



MgO = 0.540 



Na^O = 0.210 



KjO = trace 



H,0 =:= 1.460 



100.307 



VII. WlLLEMITE. 



A few specimens of this rare mineral have been discovered by Mr. J. C. 

 Cooper, of Topeka, Kansas, at the Merritt mine, Socorro county, New 

 Mexico. 



It occurs in very small hexagonal prisms, the largest not over 0.5""™ la 

 size, associated with barite, quartz, mimetite, wulfenite, cerussite and a 

 blue coating of a cupreous mineral. The willemite crystals are sometimes 

 isolated, colorless, or black with a colorless top, mostly in coatings or 

 ridges of aggregations of crystals filling cavities in the barite and quartz. 

 They show only the prismatic and basal planes, the prismatic sometimes 

 slightly striated longitudinally. In druses of quartz the microscopic 

 willemite crystals are united to clusters, the individual crystals barrel- 

 shaped, with deep longitudinal striation terminating in a serrated basal 

 plane or in a point. 



The mimetite, which is associated with the willemite, is of a bright honey 

 yellow color, crystallized in slender hexagonal prisms with pyramid, often 

 without the basal plane, also united to clusters, which, on breaking, pre- 

 sent a radiating structure. 



The wulfenite has a reddish-orange color, the crystals are tabular, and 

 show pyramids of the first and second order. 



It was difficult to obtain a sufficient amount of the willemite, and only 

 by selecting a larger quantity of the purest material, and partial crushing 

 and washing oflf the lighter particles and purifying the heavier by pick- 

 ing, I succeeded in getting enough to leave no doubt about the accuracy of 

 the mineralogical determination. 



The analyses gave : 



1 2 



Spec. grav. = 4.098 — 



Barite = 0.69 — 0.69 



SiO^ = 29.16 — 28.72 



PbO = 2.04 — 1.98 



CuO = 0.50 — 0.48 



Fe^Oj = 0.10 — 0.04 



Zno = 66.79 — 66.59 



Ignition = 1.18 — 1.18 



100.46 99.68 



Analysis 1 gave 91.53, and analysis 2, 91.18 per cent willemite. 

 Lead and copper are probably present as carbonates. 



