72 
GEOLOGY OF THE SECOND DISTRICT. 
in a few instances, as at Pitcairn and'Fowler. Asbestus, in beautiful silky veins, is abundant 
at Port Henry. Talc, so commonly connected with the beds of serpentine in Massachusetts, 
does not occur so frequently in connection with the serpentine of the northern counties. 
Neither do the minerals of the limestone, as brucite, augite and spinelle, ever occur in the 
serpentine. 
Beautiful satin spar is found in the serpentine at Pitcairn, and copper-colored mica at 
Gouverneur. The fact, however, most interesting in relation to the serpentine, is of a nega¬ 
tive character: that those substances so common, or in fact characteristic in the serpentines 
of other places, are entirely absent here ; a fact which goes far towards confirming the 
opinion already expressed, that they are of ditferent ages, or belong to different periods. The 
magnetic oxide of iron does not occur in New-York in the same state of oxidation as at Troy 
in Vermont, but it is not improbable that the specular ore takes the place of the magnetic; 
if so, the association of serpentine with the oxide of iron may be considered as a constant 
fact. The change in the oxidation of the magnetic oxide into the peroxide, is not to be lost 
sight of; for the only fact of importance is the association of an oxide of iron, its state of 
oxidation being merely an accidental circumstance. 
At Middlefield, Mass., a metallic substance like chromite of iron, is diffused very generally 
through the rock. Some of the particles are probably the magnetic oxide, and others the 
chromite. In 1820, dodecahedral crystals of the magnetic oxide in the serpentine were dis¬ 
covered by myself, associated with massive chromite of iron and pseudomorphic crystals of 
steatite. 
5. Rensselaerite. 
In placing this substance among the rocks of New-York, I have been governed by the prin¬ 
ciple, that all masses which exist independent of veins and disseminated particles, or crystals, 
should be ranked with the rocks proper, though they may be quite limited in extent, and con¬ 
fined, so far as discoveries have been made, to the northern counties of New-York. Rens¬ 
selaerite, though not strictly a new substance, was separated from steatite, or soapstone, in 
the report for 1837.* It had been employed under that name for many years, for the manu¬ 
facture of inkstands, and several other small domestic articles. Their use, however, had been 
confined mostly to a small section of country; and in consequence of being cut, and imper¬ 
fectly polished, they appeared much like the common steatite, which was in use for similar 
purposes. Though there is a resemblance, yet, in fresh quarried specimens, the rensselaerite 
does not exhibit that flaky appearance so characteristic of steatite ; and it required only a 
slight examination, to discover that it differed materially from soapstone. 
Considered as a mineral species, rensselaerite possesses the following properties : Hard¬ 
ness equals 3.5 to 4.0, or between calcareous and fluor spar : specific gravity, 2.874. The 
crystalline form under which it appears, is an oblique rhombic prism, of the same measure- 
Appendix to the Report of the Second Geological District, p. 154. 
