80 J. P. Rowe — Pseudomorphs and Crystal Cavities. 



Art. XIII. — Pseudomorphs and Crystal Cavities; by J. P. 



Rowe. 



Some of the finest pseudomorphs and crystal cavities the 

 writer has ever seen came to his notice recently from specimens 

 collected near Shoshone, Idaho. The material was collected and 

 sent to the University of Montana by Rev. T. L. Lewis. The 

 natural mineral is pyrite, imbedded crystals ; the pseuclo- 

 morph, limonite ; and the matrix, a fairly pure, light colored, 

 quartzite. 



Specimens were found showing the unaltered pyrite cubes 

 below imbedded in pure homogeneous quartzite, the pseudo- 

 morphs of limonite above in the same material, and still higher 

 the beautiful and perfect cavities, where the pseudomorphs had 

 been dissolved out by the action, probably, of meteoric water. 

 Almost all of these cavities show the delicate striations of the 

 pyrite cubes. The matrix is literally filled with these cavities 

 and presents a regular honeycombed appearance. The size of 

 the cavities range from *15 of a centimeter in diameter to. 2*5 

 centimeters. However, but few if any of the cavities are per- 

 fect cubes. One of the most interesting things about these speci- 

 mens is, that the distance from the pyrite crystals to the crystal 

 cavities, i. e. including the pseudomorph limonite, in many 

 instances, is not more than five centimeters. In fact, in many 

 cases the pseudomorphs are not more than 1*5 to 2 centimeters 

 from the pyrite crystals. 



£2 



£ 



Taking it all in all the specimens are very beautiful. They 

 show the transition of the pyrite to the limonite as do but very 

 few specimens. They also show that limonite is easily soluble 

 in certain kinds of water. They still show how these cavities 

 might be refilled with quartz or calcite or some other mineral 

 from solution and again give false forms, not true pseudomorphs 

 as in the first instance, but so to all appearances. 



University of Montana, Missoula, April 29, 1904. 



