238 Exiractsfrom the third Volume of 



is found Interposed in an insulated state, in light brov^'lt 

 pellucid crystals. 



The specific gravity of this zirconia is 4485. 

 It is perfectly infusible, and does not lose its colour by 

 calcination. It contains 



Zirconia - - - 65 



Silex - - - - 33 

 Oxide of iron • - I 



99 



Analysis of Madreporite. 



Madreporlte, belonging to the class of calcareous stones, 

 found by M. de Molle some years ago at Russbachtlial, in 

 the country of Salzbourg, is a stone of transportation. Some 

 specimens weigh from twenty to thirty pounds. 



Externally it resembles basaltes so much that some mi- 

 neralogists considered it, at first, to be the same. Others 

 have believed that it was produced from madrepores. But 

 it exhibits no certain characters of a primitive organic for- 

 mation. Besides, it has such a great resemblance to the 

 real madreporites that it has thence borrowed its name. It 

 is of a gray colour : it is composed of divergent prisms, 

 brilliant on their transverse fracture, and of a black and 

 duller colour ©n the longitudinal fracture. The fracture ex- 

 hibits a tissue of small bent laminae. It is entirely opake, 

 brittle, rough to the touch, and of moderate hardness. 

 The intervals between the buudles which compose it are in 

 part filled with small white leaves of calcareous spar. 



According to the analysis of M. Molle, a hundred parts 

 of this madreporite contain 



Analifm 



