HYDROUS SILICATES. 315 



grayish-green to dark olive-green color, and pearly lustre. 

 G.=2-7. 



Composition. A hydrous silicate of aluminum and iron 

 With little or no alkali, and in this last point differing from 

 pinite. An average specimen afforded Silica 44*00, alumina 

 30*10, iron protoxide 3*86, manganese protoxide 2*24, mag- 

 nesia G'75, lime 1*35, potash 1*98, water 9*35 — 100*23. 

 B.B. fuses to a white glass. In a closed tube gives water. 

 Insoluble in acids. 



Diff. It is distinguished from talc by affording much 

 water before the blowpipe, and readily by its association 

 with iolite, and its large hexagonal forms, with brittle folia. 



Obs. Fahlunite has been derived from the alteration of 

 iolite. The quantivalent ratio of iolite for the protoxides, 

 sesquioxides, and silicon is 1:3:5; and for fahlunite, the 

 same, with 1 for the water, making the whole 1:3:5:1. The 

 hydration appears to go on at the ordinary temperature, 

 and in some localities all the iolite to a considerable depth 

 in the rock is changed to fahlunite. There are different 

 varieties, depending on the amount of water, and the con- 

 ditions under which the change has taken place. The 

 names they have received are Hydrous Iolite, Chlorophyllite, 

 EsniarJcite, Aspasiolite, Pyrargillite, Triclasite. Fahlunite 

 was so named from its locality, Fahlun, Sweden ; and Chlo- 

 rophyllite from its greenish color and foliated structure ; the 

 specimens to which it was given occurring at Unity, N. H. 

 Haddam, Ct., is another locality. Gigcmtolite, Iberite, are 

 also altered iolite, but they contain potash, and belong 

 hence to the Pinite Group. 



Hisingerite. 



Massive ; reniform ; of a black to brownish-black color, 

 yellowish-brown streak, greasy lustre inclining to vitreous. 

 H.=3. G. =3-045. 



Composition. A hydrous iron silicate. Silica 35-9, iron 

 sesqnioxide 42*6, water 21-5 = 100. But in some analyses 

 part of the iron is in the protoxide state. B.B. fuses with 

 difficulty to a magnetic slag. 



Obs. From Sweden, Norway, Finland. Scotiolite and 

 Degeroite are referred to it. Melanolite, from Milk-Kow 

 quarry, near Charlestown, Mass., is related in composition, 

 if the material analyzed was a pure species. 



