452 PROCEEDINGS OF THE AMERICAN ACADEMY. 



II. LEADHILLITE FROM NEVADA. 

 By C. Palache. 



The results of the investigation of leadhillite from Utah are confirmed 

 and extended in an interesting manner by the study of another occur- 

 rence of the mineral recently brought to light by Dr. T. A. Jaggar. In 

 the course of an examination of the Quartette Gold Mine, at Search- 

 light, Lincoln County, Nevada, Dr. Jaggar collected specimens of the 

 ores which were submitted to the writer for determination of some of the 

 constituent minerals. Much of the ore at present worked is massive 

 cerussite; imbedded in this substance glistening cleavage plates of a 

 pale green mineral #vere noted which proved to be leadhillite. Careful 

 search revealed a single cavity in the cerussite, lined and partly filled 

 by interlaced tabular crystals of the mineral, which though very small 

 and for the most part fragmentary, proved to be very well adapted to 

 measurement and yielded a surprisingly rich form series. 



The other minerals of the ores of this mine are, first and most im- 

 portant, free gold, which occurs in visible particles in a quartz vein-stuff 

 brilliantly stained with blue chrysocolla. Wulfenite is also found im- 

 planted on quartz in crystals of two types, one pale yellow with cubical 

 habit showing the forms m (110) ^ (430), n (111), e (101), and c (001) ; 

 the other in deep red tabular crystals showing the forms 1 (740, 

 e (101), u (102), n (111) and s (113). In a few cavities in massive 

 gray cerussite were crystals of cerussite with the forms b (010), c (001), 

 m (110), x (120), y (013), i (021), z (041), y (102), and e (101). 

 Many ore surfaces are covered with a drusy black coating, greenish 

 when rubbed, which proves to be cuprodescloizite in crystals too mi- 

 nute to be interpreted. Calcite, malachite, and hematite are abundant 

 in crevices of the brecciated vein material and wall-rock. Sulphide 

 ores, except minute amounts of galena, have not yet been met with in 

 the mine. 



The crystals of leadhillite are always tabular, and most of those 

 measured had one or both of the basal planes as crystal faces rather 

 than as cleavage. The tiny tables, rarely more than a millimeter 

 across, were attached to the cavity wall by an edge and projected 

 freely, so that faces were present in both upper and lower octants, re- 

 quiring two adjustments on the goniometer for complete measurement. 

 Some seventeen crystals were measured, and yielded the forms shown 

 in Table III. The crystals proved to be largely free from twinning, 

 and when twinned the two individuals were in contact rather than 

 interpenetrating, so that the interpretation of the results of measure- 



