498 Heivett and Shannon — Orientiie, a neiv 



Calpite is present in many deposits near Bueycito, and 

 uniformly is the latest mineral. It occurs as short 

 , scalenohedrons terminated by fiat rhombohedrons which 

 line drusy cavities and commonly rest upon one of the 

 zeolites. ElseAvhere it fills the space remaining after the 

 other minerals were deposited (fig. 1). 



It should be noted that in the Bueycito region orientite 

 and the other silicates susceptible of decomposition by 

 weathering are uncommonly fresh and that the ordinary 

 products of weathering characteristic of residual deposits, 

 wad, variegated clays, etc., are practically absent. In 

 general the rocks adjacent to the bodies of manganese 

 oxide and orientite are quite fresh. Burchard, however, 

 has described'-' several deposits, such as those near Palma- 

 rito, where manganese oxides are imbedded in clays 

 that lie in solution cavities in limestone. 



Summary of Paragenesis. — In the Bueycito region, the 

 several minerals that make up the manganese ^leposits 

 have been deposited by the replacement" of latite tuffs. 

 Here and there, in parts of some of the richer deposits, 

 the tuffs have been completely replaced and no traces of 

 the original minerals remain. In some of the poorer 

 deposits however, and on the borders of all of the 

 deposits, replacement has been selective; the fine matrix 

 of the tuff's in general is replaced by oxides of manganese 

 and the glassy fragments and calcareous fossils are 

 replaced by orientite. The feldspars resist replacement 

 in this zone. 



From the study of thin sections and polished opaque 

 sections the following tentative order of genesis is indi- 

 •cated : 



Beginning of -^n.l of 



deposition deposition 



Bayate ■ — 



Glauconite 



Psilomelane 



Mauganite (plumose) 



Barite — 



Orientite • _^ 



Mang'anite (prisms) 



Quartz 



Zeolites 



Calcite 



Burchard, E. F., loc. cit., p. 25. 



