RENSSELAERITE. 
73 
merit as pyroxene. Cleavage, or natural joints, parallel to the terminal planes. The •wea¬ 
thered surface is softer than the interior, and is often easily cut with a knife, or scratched 
with a nail. Color usually grey, with shades of red, green or yellow ; but it is sometimes 
so dark as to appear nearly black, or a very dark brown or green. Structure compact, slightly 
crystalline, though the individuals are not perfectly developed. It is also in thick fibrous 
masses, in radiating bundles, like some varieties of anthophyllite or tremolite. Distinct crys¬ 
tals of a reddish hue, occur single in granular carbonate of lime. Fracture uneven : indi¬ 
viduals strongly coherent; or, in other words, it is tough. Before the blo^wpipe, it whitens, 
and fuses with difiiculty into a white enamel ; moistened with nitrate of cobalt, it assumes a 
pale flesh red. It is found in- irregular masses and crystals, in calcareous spar, or primitive 
limestone. 
In the report for 1837, I remarked that its crystalline form differs from that of serpentine 
or talc, and that it is also considerably harder. On account of these characters, it was sepa¬ 
rated from those minerals. But its crystalline form appeared to be precisely that of pyroxene ; 
and it was impossible, with the common goniometer, to perceive a difference in the measure¬ 
ment of the angles of the crystals belonging to these two substances. It is, however, much 
softer, and of a less specific gravity ; and inasmuch as it has homogeneity and regular struc¬ 
ture, it appears proper to keep it separate from that mineral also. It has a close alliance to 
serpentine, but is harder, and its crystalline form makes it quite distinct from that also. Its 
name was given in honor of Stephen Van Rensselaer, a distinguished patron of science 
and learning, whose memory will long be cherished in the community in which he lived. 
Some mineralogists have supposed that the crystals were pseudomorphic; but the fact that 
they exhibit very clearly natural joints, invalidates this opinion. All pseudomorphics, in their 
external forms, are perfect; yet they are compact, and destitute of internal structure. As a 
rock, rensselaerite has a strong resemblance, as has already been remarked, to the soapstone, 
or serpentine ; though it differs in color from the latter, as it never presents those varieties of 
green ; and if green appears, it is an olive green, which I have rarely if ever observed in the 
serpentines. 
So far as I have observed, this rock is not traversed by a system of joints; and the only 
indications of a jointed structure are numerous irregular seams, disposed without order. It 
is, therefore, a mass quite amorphous as a whole, occurring in beds like serpentine or steatite. 
In consequence of the softness of this material, it is adapted to a variety of purposes. The 
white varieties are feebly translucent; and when carefully smoothed and polished, after being 
cut thin, they look very much like porcelain. It is often cut into pipe-bowls, and tea-cups ; 
and were it red, it would resemble the Indian pipe-stone, and it is possible that it is a 
substance more closely related to that curious rock than serpentine or potstone. 
Geol. 2d Dist. 
10 
