LABRADORITE AND HORNBLENDE. 
29 
is either compact, or finely granular ; so that it presents the aspect of porphyry, or a porphy- 
rytic granite. The proportions of the two forms, or states of the labradorite vary infinitely 
in proportion ; in some instances, the crystallized predominates; in others, the granular or 
compact. We find, too, in this variety the same diversity as it respects color: the granular 
is sometimes of a greenish grey, or pure smoke grey, or an iron grey ; or, when it predominates 
in the mass, it is greenish grey ; but when the crystallized, it is some shade of smoke grey. 
This variety, in any state, is a beautiful rock, even with its rough fractured surfaces ; when 
polished, its beauty is greatly increased. If cut into thin tables, and polished, it would form 
one of the most ornamental articles for parlors which can be imagined, especially those which 
are opalescent. Nothing of the kind has yet been in market ; and the expense for quarrying, 
sawing and polishing the material, cannot be determined without experiment. The rock is 
less hard than quartz. Its powder might be employed in sawing, as in marble. I have hoped 
that some one would be induced to ascertain the cost of cutting and polishing this rock, for 
the purpose of introducing it to the notice of the wealthy as a fine substitute for marble, 
which, being much softer, becomes defaced by use. 
This variety furnishes the fine specimens of that mineral which is called opalescent feld¬ 
spar, of which I have noticed among them five kinds of opalescence ; the green, blue, both 
light ahd deep, golden yellow, the bronze, and that in which the green and blue are arranged 
in stripes. The deep blue varieties are the most common; in fact, large masses exhibit this 
striking kind, if placed in the proper position for observing it. 
The variety which gives the green opalescence is comparatively rare. It appears, from the 
specimens of this same rock brought from Labrador, that there the green is the most com 
mon, or the golden yellow, both of which are met with in the shops of lapidaries, while the 
blue is uncommon. In the most perfect specimen, the green and blue may be seen on the 
same piece by looking in opposite directions : in one, it will be found that the light is blue; 
and in the opposite, green. It is not uncommon to meet with pieces which are truly gems, 
and which are not only valuable for their beauty, but of higher value than other gems, in con¬ 
sequence of their being inimitable by any process of art. 
The localities which furnish the opalescent feldspar, are principally the beds and banks of 
the streams and rivers which flow from the Adirondacks, especially the beautiful and extended 
beaches of the East river, which furnish abundance of very fine specimens. A locality, at 
which large cleavage pieces of the deep blue variety may be obtained, is Avalanche lake, 
near the foot of the great slide from Mount McMartin. It occurs here in large, clean masses, 
from which may be obtained good primary forms of the mineral species. A fact worthy of a 
passing notice is, that although labradorite is so constantly crystalline, and furnishes such an 
abundance in this State, it has never as yet been observed in crystals with natural faces—a 
fact which applies mostly to this substance. Those minerals, for instance, which occur in a 
crystalline state, appear also (with perhaps a few exceptions) in crystals wdth natural planes. 
Labradorite and Hornblende ,—This variety is not uncommon : it is produced by the sub- ' 
stitution of hornblende for hypersthene. When this takes place, the principal change is indi.. 
cated by a darker color of the rock ; but it is often difficult to detect the chauge.. The horn- 
