236 DESCRIPTIVE MINERALOGY. 



bath to dryness, a loose crystalline powder is obtained, which, under the microscope, appears 

 for the greatest part as an aggregation of distinct crystals, which manifestly have the form of 

 arragonite. They generally appear as six-sided columns somewhat dilated, or as very acute 

 six-sided double pyramids, hke many sapphire crystals ; at times, however, they appear as 

 single pyramids, so that they are therefore crystalUzed diflferently at the two ends. But when 

 a similar solution is allowed to stand several weeks in an open glass at common temperatures, 

 the microscopic crystals, which are found partly on the sides of the vessel and partly on the 

 surface of the solution, are always found to have the form of the primary rhombohedron of 

 calcareous spar. The method which Rose recommends for obtaining arragonite quite pure, 

 and free from calcareous spar, is to pour a hot solution of chloride of calcium into a hot so- 

 lution of carbonate of ammonia. The crystals are exceedingly minute, and have a specific 

 gravity of 2.949. 



Rose also remarks, that in order to preserve unchanged the arragonite obtained by precipi- 

 tation, it is necessary to wash and dry it immediately. If it is allowed to stand after precipi- 

 tation for any length of time in the fluid, it is in a very curious manner gradually converted into 

 calcareous spar. This metamorphosis, however, seems only to take place when the arragonite 

 is newly precipitated. If it has been well dried first, it remains quite unchanged, even if it 

 be now re-immersed in water or carbonate of ammonia, and allowed to stand in it for weeks. 



In the progress of these experiments, it was also ascertained, that when arragonite is ex- 

 posed to a low red heat, it is changed into calcareous spar, the large crystals falling in a coarse 

 powder ; the smaller ones retaining at the same time their form, and producing pseudo-mor- 

 phous crystals. 



For the purpose of still further testing the question whether the carbonate of strontia is 

 necessary to the formation of arragonite. Rose mixed a small quantity of a solution of chloride 

 of strontia with a solution of chloride of hme, but by precipitation at the common temperature 

 with carbonate of ammonia, crystals of calcareous spar only were perceivable.* 



LOCALITIES. 



Niagara County. Shepard states that, the variety called Flosferri has been found coating 

 gypsum in geodes at Lockport.t 



Orange County. Specimens of what I suppose to be arragonite, have been found in cavi- 

 ties in the magnetic iron ore at the Wilks and O'Neil mines in the town of Monroe. The 

 colour is white or yellowish white ; it is mammillary, botryoidal, fibrous, and in imperfect 

 crystals. The fibres are coarse, straight or stellated. Probably the same mineral occurs at 

 Edenville in this county, lining cavities of mispickel and cube ore. 



Schoharie County. According to Shepard, a fibrous variety of this species is found in 

 Ball's cave, where it is said to form stalagmites and stalactites ; but all the specimens which I 

 have examined, appear to me to be nothing more than calcareous spar. 



* On the Formation of Calo Spar and Arragonite. By Gustave Rose. Lmd. and Edin. Phil. Mag. &c. 3d Series. XII. iOo. 

 t Treatise on Mineralogy. I. 42. 



