118 RE-EXAMINATION OF AMERICAN MINERALS. 



A direct determination of the water gave 19.83 per cent. 

 These analyses give the oxygen ratio 2:3:2, and the formula 



3(Mg C+H)+Mg H which calculated gives 



Mg C H 



44.68 35.86 19.46 



The composition and formula are the same as obtained by 

 Kobell and Wachtmeister for hydro-magnesite from Negro- 

 ponte and Hoboken. We are not aware that this species has 

 heretofore been observed with a crystalline structure. 



10. Supposed Magnesite of Hoboken shown to be Aragonite. 



In connection with the foregoing investigations it was thought 

 that an examination of some of the anhydrous carbonates of 

 magnesia might be interesting. For this purpose a specimen of 

 magnesite from Hoboken, ~N. J., was submitted to analysis (the 

 variety referred to is that which occupies seams and cavities in 

 the Hoboken serpentine, having an aggregated fibrous structure, 

 and not unfrequently occurring in delicate needle crystals). A 

 careful qualitative examination of the needle crystals showed 

 them to be carbonate of lime, with scarcely a trace of magnesia ; 

 they have the form of aragonite. Specimens from Staten Island 

 and the vicinity of Westchester, Pa., were examined, with like 

 results. The crystals from the serpentine quarry near West- 

 chester are frequently transparent, and are among the most 

 beautiful specimens of crystallized aragonite that have been 

 observed in this country. 



11. Chesterlite, identical with Orthoclase. 



This mineral occurs in implanted crystals on dolomite near 

 East Bristol, Chester County, Pa. In physical characters it 

 resembles orthoclase, but it has been considered triclinic, and 

 Erni's analysis* gave soda as the alkali. The crystals occur 

 frequently as twins, and are often very much distorted — in 

 specimens we have examined the angle T on T varies from 

 121° to 127° — rendering it extremely difficult to determine the 

 normal value of the angle; some of the measurements would, 

 however, lead to the conclusion that it is monoclinic, since the 

 angle of cleavage is by our measurements near 90°. So far as 



* Dana's Mineralogy, 3d ed., p. 678. 



