SILICA. 299 



quently they are massive, and in radiated fibrous and granular concretions. The lustre is 

 vitreous or pearly, and they vary from transparent to opaque. 



Tremolite — Grammatite. The colour of this variety is white, occasionally with a tinge of 

 grey, green or blue, but lighter than actynolite. It occurs in masses composed of delicate 

 crystalline fibres, which sometimes radiate. Lustre shining or glistening, and pearly or vitreo- 

 pearly. Ranges from translucent to translucent on the edges. Before the blowpipe, it fuses 

 into an opaque white enamel. 



Ashestus. Under this term there are no doubt now arranged several distinct minerals, the 

 form of flexible silky fibrous concretions being in many cases the result of atmospheric agen- 

 cies. The colour of the hornblende asbestus is various. When the fibres are long and slender, 

 are easily separated and more or less elastic, they form the Amianthus. Other varieties, 

 which are of a white or grey colour, and have the fibres interlaced so intimately as not to be 

 capable of separation, and so light as to float in masses on water, are called Mountain Cork. 

 When the colours are green, and the fibres are disposed in straight, shining, pearly, rigid, 

 fibrous concretions, the name Rigid or Common Asbestus is applied. And those varieties in 

 which the colour is wood-brown, and in general aspect much resembling fossil wood, are 

 named Rock-wood, or Ligneous Asbestus.* 



Composition. The different varieties diflfer somewhat in their chemical composition. 



Black Hornblende — Silica 45.69, magnesia 18.79, lime 13.85, alumina 1.18, protoxide 

 of iron 7.32, fluoric acid 1 .50 {Bonsdorf). 



(xreen Hornblende — Silica 46.26, magnesia 19.03, lime 13.96, alumina 14.48, protoxide 

 of iron 3.43, protoxide of manganese 0.36, fluoric acid 1.60, water, etc. 1.04 (Bonsdorf). 



White Hornblende — Silica 60.31, magnesia 24.23, lime 13.66, alumina 0.26, protoxide 

 of iron 0.15, fluoric acid 0.94, water and foreign matter 0.10 {Bonsdorf). 



Amianthus — A variety with a greenish-white colour — Silica 55.91, magnesia 27.07, lime 

 14.63, alumina 1.82, protoxide of iron 6.52 {Thomson). 



Geological Situation. Hornblende abounds in the primary regions of the State, and is 

 rarely found elsewhere, unless associated with trappean rocks. Hence the most important 

 localities occur in the southern and northern counties. It is especially abundant where beds 

 of white limestone or dolomite occur in the primary ranges, and the presence of hornblende 

 is usually an indication of the existence of other minerals in the vicinity. 



As there are very numerous localities of this mineral in this State, I shall only introduce 

 those which aflford well characterized specimens of one or other of the varieties. 



LOCALITIES. 



Dtjtchess County. Near a hamlet called Peckville, in the town of Fishkill, there is a 



* Mr. Allan correctly remarks, that greatly as black crystallized hornblende and white silky asbestus differ in aspect, speci- 

 mena exist in which the passage of the one into the other is distinctly risible. Manud of Mineralogy. 



