192 proceedings of the academy of [1888. 



July 3. 



Mr. Thomas Meehan, Vice-President, in the chair. 



Ten persons present. 



Note on Mazapilite, a new species. — Prof. Geo. A. Koenig an- 

 nounced the occurrence of this mineral at Zacatecas, Mexico, in the 

 mineral district of Mazapil. The crystals are well developed in 

 all directions. They are of orthorhombic symmetry exhibiting a 

 flat prism in combination with a brachy dome and a pyramid. The 

 color is deep brown red, nearly black, but transparent at the edges. 

 The hardness is nearly 7, its streak greenish yellow. The specific 

 gravity 3*567. In closed tube a white crystalline sublimate is pro- 

 duced (As ^ O ^) and water, while the powder turns dark brown. 

 B. B. fuses at 3 to a black globule. On charcoal the odor of arsenic 

 is observed. With borax only iron reaction. Easily soluble in 

 in warm HCl. A preliminary analysis proves the mineral to be 

 a calcium ferric arsenite. The structural formula must be made the 

 subject of a moi'c thorough investigation, which the speaker pro- 

 poses to carry out in the fall. Tliis mineral is the first representa- 

 tive of the class of pure arsenites in nature and is therefore of mark- 

 ed interest. For the material the author is indebted to the indefat- 

 igable zeal of Dr. F. A. Foote, who is now in Mexico. 



The following was ordered to be printed : — 



