141 



The following are the results of an analysis of this mineral by M. 

 Damour: Silica, 59-64; alumina, 16.33; lime, 7*44; soda, 1'16: 

 potash, 0-74 ; water, 14*33. This composition indicates that heulan- 

 dite should be ranked with the zeolites. Philosophical Mag. and Ann., 

 xxix., p. 556. 



It seems to be now settled, that the Lincolnite of Prof. Hitchcock, 

 {Final Report on the Geological Survey of Massachusetts, p. 662,) is 

 identical with heulandite. Crystals, exactly like those described by 

 Hitchcock, have been found in gneiss on New- York Island. Alger, in 

 Sill. Jour., xlvi., p. 235. 



PREHNITE. 



(Mineralogy of New-York, page 349.) 



Since the publication of the Mineralogy, this mineral has been found 



in the fissures of gneiss in 23d street, New-York. Dr. Emmons also 



reports localities near Adirondack, and in Keene, Essex county. Rep. 



on the Geol. 2d Dist., p. 31. 



LAUMONITE. 

 (Mineralogy of New-York, page 351.) 



It is well known that this mineral when exposed to the atmosphere, soon 

 loses its transparency, and becomes so soft as to yield to the finger nail. 

 According to M. M. Malaguti and Durocher, this efflorescence is owing 

 to the loss of a small quantity of water. Specimens of it did not suffer 

 the least alteration when kept for several months in a moist amosphere. 

 Crystals of laumonite altered, recovered their original transparency and 

 appearance by being immersed in water, and these same crystals, after 

 drying and exposure to dry air, behaved like crystals recently taken from 

 their locality. Phil. Mag. and dnn. xxix, p. 555. 



Dana states that the rapid decomposition to which this mineral is 

 liable may be prevented by dipping the specimen in a thin solution of 

 gum arabic, by means of which it is preserved from contact with the 

 air. Mineralogy, 2d ed.. p. 326. 



