270 North — Pseudomorphs of Limonite after Marcasite. 



Art. XXII. — Pseudomorphs of Limonite after Marcasite / 

 by H. B. North. 



Pseudomorphs after pyrite and marcasite are frequently 

 seen and those after the former mineral retaining perfect crys- 

 talline form are quite common. On the other hand, good 

 pseudomorphs after marcasite are seldom seen, the usual 

 museum specimen being scarcely more than a shapeless mass of 

 limonite, showing no definite form of the mineral before alter- 

 ation. In consideration of this it may be of interest to scien- 

 tists in general and to mineralogists in particular to learn that 

 a new find of limonite after marcasite has been made and that 

 the specimens still retain the crystalline form of marcasite. 



The new find was made in Richland County, Wisconsin, 

 across the Wisconsin river from and directly north of the lead 

 and zinc region. The mineral has been located on several hill 

 tops, all within a radius of a mile. Many of the specimens 

 were plainly visible on the surface of the ground or embedded 

 in the grass, while others were found beneath the surface to a 

 depth of 12 to 14 inches, in a sort of clay which is underlaid 

 by sand. The best specimens, obtained just beneath the sod, 

 have a dark red-brown color, a smooth hard surface and a 

 good luster. The various faces are not in the least distorted 

 and the edges are in perfect. condition. 



The specimens found on the surface of the ground are some- 

 what less brilliant in color, though in general they exhibit a 

 perfect crystalline form. On the other hand, many of the 

 crystals obtained from the layer of clay do not show a smooth 

 surface but appear to have been etched to a slight extent. 

 These specimens do, however, show perfect crystalline form. 

 On one particular hill top on which the soil was very sandy, 

 all specimens found have a yellowish brown coating. Several 

 unusually fine specimens were found in this locality and many 

 of the crystals exhibit faces not found on the specimens from 

 the nearby hills. 



The accompanying illustrations have been made from photo- 

 graphs of several of the better specimens. Fig. 1 (two-thirds 

 natural size) shows the finest, though not the largest specimen 

 found, the individual crystals being slightly larger than those 

 on any of the other specimens. This specimen is 14*5 cm long 

 and stands 7'5 cm high. It exhibits a parallel growth of 10 

 large crystals, the largest of which is 4 cm wide and 4 cm high. 

 The specimen weighs 715 gms. The specimen shown in £.g. 2 

 (two-thirds natural size) consists of a single and remarkably 

 fine crystal surrounded at the base by several small crystals. 

 The color of this specimen is a rich red-brown and the surface 



