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. 
Asbestus. 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 differ 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). 
Green 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, w r ater, 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 {BonsdorJ). 
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 afford well characterized specimens of one or other of the varieties. 
LOCALITIES. 
Dutchess 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¬ 
mens exist in which the passage of the one into the other is distinctly visible. Manual of Mineralogy. 
