Pirsson and Wells — Occurrence of Leadhillite. 219 



Aet. XXXI. — On the Occurrence of Leadhillite in Missouri 

 and its Chemical Composition • by L. Y. Pirsson and H. L. 

 Wells. 



Leadhillite, the hydrated sulphato-carbonate of lead, is a 

 rare mineral, occurring in but a few places in Europe and hav- 

 ing been reported from but three localities in this country.* 



It is therefore a matter of interest to announce a new occur- 

 rence in America, and as the exact chemical composition of the 

 mineral has been uncertain and the material is well suited 

 for mineralogical and especially for chemical investigation, 

 these have been undertaken with the results given in the pres- 

 ent article. 



Our atteution was first called to this occurrence by Messrs. 

 English and Co., of ~New York City, who sent us some speci- 

 mens for identification and we take great pleasure in expres- 

 sing our thanks to these gentlemen for the very liberal 

 manner in which they have placed an abundant supply of fine 

 material at our disposal for this investigation. 



The mineral occurs near Granby, Missouri, and has been 

 probably formed by the action of water, carrying carbonic acid 

 and oxygen in solution, on galena. 



The specimens which we have studied consist of masses and 

 crusts often apparently pseudomorphous after the original lead 

 ore and consisting mainly of massive cerussite, mingled possi- 

 bly with other lead salts. The leadhillite occurs implanted 

 upon this in well defined crystals or in aggregated groups 

 studding the interior of cavernous portions of the amorphous 

 crusts. 



The isolated crystals are often quite perfect, in rather 

 slender, apparently hexagonal prisms attaining a length of 

 50 mm and terminated at either end by the basal plane. More 

 commonly, however, they occur in rather thick hexagonal 

 tables, at times l cm in breadth, numbers of which are grouped 

 together in parallel position or consisting of repeated twins. 

 When these occur lining cavities only the front half of the 

 crystals are often developed, and as they extend to right or 

 left or rise one above the other, all in parallel position, they 

 represent in miniature precisely the appearance shown by 

 columnar cliffs of basalt whose broken off hexagonal columns 

 rise step-like above each other. 



In these cavities they are often associated with slender, 

 striated, glittering prisms of cerussite, occurring at times in 

 fine twins, the twinning plane being the prism r (130). 



* Newberry Dist. ; Spartanburg Disc. No. Oar. by Shepard and from the Schultz 

 gold mine in Arizona, by Penfield, cf. Dana's Min. 6th ed., p. 922, 1892. 



