On the Strontianitc of Schoharie, (N. Y.) 



365 



in veins, from a quarter of an inch, to two inches wide, and is em- 

 braced directly by clayey limestone. Rarely, it is traversed by 

 large lamellae of Heavy Spar, which are easily distinguishable by 

 their crystalline texture. Very small quantities of Calcareous Spar 

 attend this variety occasionally, but it is not of a blue color. The 

 circumstances of its deposition appear to have been different from 

 those»of the first variety. The two varieties described were forward- 

 ed in the first box. 



A third and more interesting variety came in the second box, of 

 which Mr. Bonny remarks, that it was discovered since the date of his 

 first letter. From the specimens before me, it appears to form a vein 

 of considerable size, the mass of which resembles the last variety in 

 structure and color, as well as In being traversed occasionally by 

 lamellae of Heavy Spar. But upon one side of the masses, tabular 

 crystals of Strontianite single and compound, an inch in length, and 

 one third of an inch wide, are thickly implanted on a surface of 

 transparent crystals of Calcareous Spar. The Calcareous Spar is 

 in large crystals of the form of the metatastique. The Strontianite 

 is partially coated by a white powder, as if it were suffering decompo- 

 sition,* and the crystals of Calcareous Spar are covered completely 

 by little fissures and cavities, where the Strontianite once penetrated 

 them. It is observable however, that the large crystals of Strontian- 

 ite still remaining are connected among themselves, as also to the 

 mass of massive Strontianite below. Small transparent crystals of 

 Quartz are also disseminated through the Calcareous Spar, but no 

 Iron Pyrites is present. Figure 1, represents the form of these 

 crystals. oono=160^. It will be observed that the edge be- 

 tween these faces corresponds to P, or the terminal plane of the 

 primary prism ; while the horizontal edge between c c corresponds to 

 M of the same figure. 



Fi^. 2. 



Fig. 3. 



* The only suggestion that offers itself to my mind in explanation of this incip- 

 ient decomposition is, that sulphuric acid may have been produced from the oxyd- 

 ation of the sulphur in the Iron Pyrites, and have formed a slight coating of sul- 

 phate of stronlita upon the crystals of the Strontianite. 



