232 



University of California. 



[Vol. 3. 



intergrowth, more or less parallel, of smaller individuals. The 

 superintendent of the mine, Mr. J. B. Mason, who found the 

 mineral and has kindly sent specimens to the writer, reports that 

 the red sulphate was found by cross-cutting through an old stope 

 which had been filled about forty years ago, the mineral having 

 formed in this stope with newly formed cinnabar and much 

 sulphur. The heat developed from the decomposition of the 

 marcasite was so intense where the mineral occurred, that the old 

 timbers of the stope had become converted into solid charcoal. 

 The specimens sent to the writer had much yellow sulphate asso- 

 ciated with them, which is probably copiapite, although this has 

 not yet been definitely proved. 



This mine is quite noted for the variety of sulphates formed 

 from the decomposition of the sulphides, epsomite, knoxvillite and 

 redingtonite,* and coquimbitef having previously been described 

 from there. 



C'R YSTALLOGRAPHIC CHARACTERS . 



Measurements. — The crystals were measured principally by 

 the two-circle method, although a few interfacial angles were 

 also determined. The larger crystals, owing to their composite 

 structure, give poor measurements, the prism faces being striated 

 and often interrupted, and the bases wavy; but some of the 

 smallest crystals, about 1 mm. in size, gave very exact readings, 

 and these were chosen for the calculations. 



System and Habit. — The crystals are monoclinic and have but 

 one habit, namely, short prisms terminated by the two basal 

 planes. The prismatic zone and the base are in almost equal 

 development, and the crystals in consequence resemble rhombo- 

 hedrons . 



Polar Elements and Axial Ratio. — The average values of p'o, 

 g'o and e determined from the coordinates % and xj , for the 

 prisms, clino-domes and bases, were as follows: 



p' = 0.6852 ; q '„ = 0.3996 ; e = 0.5128. 

 *Melville and Lindgren, U. S. Geol. Surv. Bull. 61, 1890. 



tA. S. Eakle, Mineralogical Notes, Bull. Dept. Geol., Univ. Cal., Vol. 2, 

 315-326, 1901. 



1 



