May, 1904. GEOLOGY OF WESTERN MEXICO—FARRINGTON. 215 
facets, terminated by an irregular pyramid of six faces, of which 
two or three are often imperfect or wanting, These crystals are 
said to be often confounded in Durango with topaz. 
Of the above, only martite, quartz, chalcedony, and opal were 
collected or observed by the writer. Apatite, however, was collected 
on the mountain by S. E. Meek of the Museum in 1903, and an ex- 

Fic. 4. Martite. Cerro Mercado. x1. 
cellent suite of these crystals now forms a part of the Museum col- 
lections. 
The martite collected by the writer (Mus. No. M 5497) was in 
the form of simple crystals attached to masses of the solid ore. The 
appearance of a typical specimen is shown in Fig. 4. The specimens 
were all obtained from the west side of the mountain, where the 
crystals occurred in groups, generally lining cavities. The crystal form 
was invariably that of unmodified octahedrons. In size the crystals 
varied from those measuring only a millimeter on a side to some 
measuring twenty to twenty-five millimeters. Their color was 
iron-black, with occasional coatings of brown iron oxide. None 
of the crystals nor their powder was attracted by the magnet, the 
behavior of the powder in this respect differing from that examined 
by Silliman. The color of the streak and powder was the familiar 
