LEDOUXI AURICHALCITE 363 



ments. Aurichalcite has thus been considered ortho-rhombic, 

 monoclinic, and triclinic. 



Professor A. Lacroix 6 agrees with Prof. Cesaro in regarding 

 aurichalcite as orthorhombic. He suggests that Professor d' 

 Achiardi in regarding the mineral as monoclinic on account of 

 an extinction of 17° may have made his observations on plates 

 seen obliquely to the cleavage. The aurichalcite from Chessy, 

 France, occurs as needles without flattening, with parallel ex- 

 tinction, suggesting orthorhombic symmetry. 



Chemical examination of aurichalcite from Utah has been 

 made by Penfield, 7 who deduced the formula 2(Zn, Cu)C0 3 . 

 3(Zn, Cu) (OH)o. If Zn : Cu = 5:2, the theoretical composition 

 is as following: 



C0 2 16 . 14 



CuO 20 . 79 



ZnO 53.17 



H 2 9.90 



100.00 



Penfield did not give any information about the geometrical 

 properties of the material analysed. 



The mineral aurichalcite is pale blue to pale green in color, 

 appearing macroscopically to consist of delicate aggregates of 

 bluish needles; under the microscope, however, the needles 

 commonly appear as wedges with a very acute angle a. Some- 

 times the wedge has the form of a right-angled triangle, but 

 generally the shortest side, opposite the angle a, is replaced by 

 an irregular line (fig. 1). 



On account of the uncertainty of the symmetry of aurichal- 

 cite, I thought it of some interest to make further investigation 

 of its crystals. Some very fine specimens from Big Cotton- 

 wood Canyon, Salt Lake County, Utah, were placed at my dis- 

 posal by the Royal Ontario Museum of Mineralogy. The struc- 

 ture is usually radial or plumose. To study the mineral it is 

 first of all necessary to get simple individuals; these are most 

 easily obtained by crushing an aggregate between two glass 



6 Mineralogie de la France et de ses colonies, 3: 739. 1909. 

 » Amer. Journ. Sci., Ill, 41: 106. 1891. 



