318 ' DESCRIPTIVE MINERALOGY. 



St. Lawrence County. Spinelle of a liglu blue colour, and having ihe primary form, 

 occurs associated with chondrodite, about two miles north of the village of Somcrville in the 

 town of Rossie. The crystals, however, are quite small. 



It is a singular fact, that while spinelle is so very abundant in various parts of Orange 

 county, it should be so rarely met with in the similar formations in the northern parts of the 

 State. Although it is found in the counties of Jeiferson and St. Lawrence, and, according to 

 Dr. Emmons, also in the counties of Essex and Warren, the crystals are often minute, and 

 always, as hitherto observed, sparingly disseminated ; so that it may be still said to be rare 

 in Northern New-York. 



APPENDIX. 



Soft Spinelle. There is a mineral found in the town of Warwick in Orange county, which 

 is of a black colour, and has the crystalline form of spinelle. It is imbedded in a gangue 

 of dark coloured soft serpentine. The octahedral crystals are so soft that they can be easily 

 scratched with a knife, and reduced to a coarse powder ; but the powder, which is of a grey 

 colour, is gritty, and is with difficulty rendered impalpable. 



This mineral has passed under the names of kerolite pseudomorphous of spinelle, pseudo- 

 lite, etc., which have been employed to express the supposed chemical constitution and the 

 crystalline form. 



In conducting the analysis of this mineral, I found that a large proportion of the powder 

 jesisted two or three ordinary fusions with carbonate of soda. This led me to suspect that it 

 might contain a portion of real spinelle, instead of its being, as I had supposed, entirely 

 made up of serpentine or some similar mineral. The correctness of this view was confirmed 

 by subsequent examinations. 



The composition of these crystals is nearly as follows, viz : 



Silica, 19.07 



Alumina, 35.00 



Oxide of iron 9.97 



Magnesia, 28. 58 



Water, 7.33 



If now we take about 17 parts of the silica, 15 of magnesia, 6 of water, and 2 of oxide of 

 iron, they will produce about 40 per cent, of serpentine, and the remaining constituents will 

 be nearly in the proportion in which they are found, according to the most trustworthy ana- 

 lyses, to occur in spinelle. 



The peculiarity of these crystals is therefore to be referred to the intrusion of the serpentine 

 into the crystals of spinelle, a part of which has been removed. And although the crystals 

 are softer than might be supposed from their composition as above stated, it is quite probable, 

 that during the process of substitution, the cohesion of all the particles has been impaired, 

 so as to briflg about the apparent softness of the crystals, while the particles are really so 

 hard, as they prove to be when subjected to the action of the pestle. 



