~ 
HYDROUS SILICATES. BS 
grayish-g green to dark olive-green color, and pearly lustre. 
sneer 
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°60, alumina 
30°10, iron protoxide : 3°86, manganese protoxide 2°24, mag- 
nesia 6°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 tale 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 quantiyalent ratio of iolite for the protoxides, 
sesquioxides, and silicon is 1:3:5; and for ae the 
same, with 1 for the water, making the whole 1:35:5:17. The 
hydration appears to go on at the ordinary ieee praca 
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. ‘he 
names they have received are Hydrous Iolite, Chlorophyllite, 
Esmarkite, Aspasvolite, Pyrargillite, Tr iclasite. Fuhlunite 
was so named from its locality, Fahlun, Sweden ; and Chlo- 
rophyliite from its greenish color and foliated structure ; ; the 
specimens to which it was given occurring at Unity, N. H. 
Haddam, Ct., is another locality. Gigantolite, Lberite, 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. 
feo, -G.=3°045. 
Composition. A hydrous iron silicate. Silica 35-9, iron 
sesquioxide 42°6, water 21:°5=100. But in some analyses 
part of the iron is in the protoxide state. B.B. fuses with 
(lifficulty to a magnetic slag. 
Obs. From Sweden, Nor way, Finland. Scotiolite and 
Degeroite are referred to it. Melanolite, from Milk-Row 
quarry, near Charlestown, Mass., is related in composition, 
i# the material analyzed was a pure species. 
