506 Heiuett and Shannon — Orientite. 



ness is 2.5. Under the microscope the powder is in part 

 composed of a clear light-brown isotropic material the 

 mean index of refraction of which is 1.55. In selecting 

 material for analysis it was possible to avoid silica which 

 occurs along cracks but the analyzed powder showed a 

 large proportion of black opaque oxide as well as a consid- 

 erable proportion of a fine-grained crystalline mineral 

 thought to be orientite. The analysis gave the following 

 results : 



Analysis of amorphous material. 



CaO ^ " 4.36 



MnO 20.91 



Mn.Og 21.31 



Fe.rOo (-f ALOo) 4.50 



SiO/' ". .'. 23.76 



H.d-f 110°C 8.20 



H;o — llO'C 15.60 



Insoluble 1.24 



Total 99.88 



The material is a typical colloid and the water content 

 is extremely variable, a considerable portion being lost 

 over sulphuric acid in a desiccator. The above analysis 

 may be interpreted as an orientite in which the lime has 

 been replaced largely by manganous oxide. This leaves 

 a considerable excess of both manganous and manganic 

 oxides together with the large excess of loosely held 

 water. If the lime be deducted as orientite and the triva- 

 lent bases be set aside, the remaining constituents give the 

 ratios of neotocite. In view of the colloid nature of the 

 substance as well as its manifest impurity it appears best 

 to avoid further discussion of the analysis at this time. 



