W. H. Melville — Metacinnabarite from California. 291 



Aet. XXXVIII. — Metacinnabarite from New Al?nade?i, Cal- 

 ifornia ; by W. H. Melville. 



An" excellent specimen of metacinnabarite was recently 

 found in the quicksilver mine at New Almaden, Santa Clara 

 County, California, and a portion of it was given me for ex- 

 amination. Metacinnabarite was never before known to occur 

 in these deposits, although in neighboring cinnabar localities 

 the amorphous mineral has been met with. This specimen 

 carries finely developed and brilliant crystals which are admir- 

 ably adapted for measurement on the goniometer. 



In the ore seam where cinnabar has been deposited, there 

 appears an argillaceous mass which has resulted from sediments 

 derived from the decomposition of the country rock by sol- 

 fataric action. This mass is not homogeneous but consists of 

 gray and green particles, the former evidently a mixture of 

 clay and partially decomposed rock constituents with a small 

 amount of carbonates, the latter a silicate the composition of 

 which is shown in the following analysis. 



Analysis of the Green Silicate. ■ 



Si0 2 67-59 



Cr 2 3 5-31 



Fegl -- 12 - 24 



NiO . 4-57 



CaO .... • . 0-73 



MgO 7-84 



Alkalies very little 



98-28 



In justice to these figures it should be said that only 0*1225 

 gram of substance could be obtained in sufficient purity for 

 study, and the little impurity which this sample contained 

 could not be removed by Thoulet's solution ; also alkalies could 

 not be determined. 



Throughout this sheet of soft argillaceous matter, or selvage, 

 large quantities of metallic quicksilver easily seen by the 

 naked eye are distributed, and bright red cinnabar often deeply 

 coloring small areas of quartz has crystallized. Cinnabar is 

 found mainly deposited on this selvage — on the specimen at 

 hand about an inch thick — intimately mixed with quartz, thus 

 forming a hard compact mass upon which have grown cinnabar 

 crystals, and these in turn are coated with minute quartz crys- 

 tals. To this quartz the acute apex of the metacinnabarite 

 crystal is attached and consequently is always broken. The 



