192 



University of California. 



LVOL. 3. 



INTRODUCTION. 



A small body of pyrite occurs near Leona Heights, Ala- 

 meda Co., Cal., containing some chalcopyrite, and the ore has 

 been mined for a number of years for the manufacture of sul- 

 phuric acid. In consequence of the oxidation of the sulphides, 

 several secondary sulphates of iron and copper have been 

 formed in and about the mine, and specimens of these secondary 

 minerals have been collected and studied by the writer. These 

 natural vitriols occur in such good crystals that an interesting 

 crystallographic study can be made of them. Our present 

 crystallographic knowledge of these sulphates has been largely 

 dependent on the study of artificial crystals. 



All of the minerals found at this locality, with one exception, 

 were identified with known species. These are Pyrite, Chalco- 

 pyrite, Copper, Melanterite, Pisanite, Chalcanthite, Copiapite, 

 Epsomite, Hematite, Limonite and Alunogen ( f ) . Besides these, 

 a copper sulphate with seven parts of water, Boothite, to be 

 described later, was also observed. Of these pyrite, melanterite, 

 pisanite, chalcanthite and boothite occur in good measurable 

 crystals. Copiapite occurs, to some extent, in crystals, but they 

 are all microscopic. 



The crystals were measured with the two-circle goniometer, 

 except a very few fragments, which were broken in such a 

 manner as to render their setting up in true polar position 

 impossible. The forms on these fragments were, consequently, 

 determined from measurement of the interfacial angles. While 

 many of the faces gave excellent reflections, the ratios obtained 

 from the two-circle readings were, with one exception, not con- 

 sidered as more accurate than those previously obtained. The 

 one exception is pisanite, for which elements were calculated 

 from the readings. These, it is thought, approximate more 

 closely to the true elements than those which heretofore have 

 been accepted for pisanite. 



In the chemical analyses the iron was determined by titration 

 with potassium permanganate, with occasional checks by weigh- 

 ing the iron as ferric oxide. The copper was determined by 

 iodometric titration. The water was weighed directly in a 



