92 
AMERICAN GEOLOGY. 
RENSSELAERITE. 
§ 66. This rock has been, regarded by a few of our geolo¬ 
gists as a pyroxenic steatite. It is however perfectly homo¬ 
gen eous, and w T hen the circumstances were favorable for 
crystalization, it is traversed by distinct joints, by which it is 
clearly a cleavable substance in the mass. Its hardness is 
3*5—4, and hence is greater than steatite and less than pyrox¬ 
ene; its specific gravity is 2'874. It is composed of 
Silica, 
59-75 
Magnesia, 
32-90 
Lime, 
1-00 
Peroxide of iron, 
3-40 
Water, 
2’85 
It resembles serpentine in the structure of the mass, but its 
particles of composition are coarser and more crystalline. It is 
white or grayish white, and tinged faintly with green. Black 
varieties are not uncommon. It is traversed by irregular 
seams of satinspar, disposed without order. It is massive, 
and its lamination is obscurely brought out by weathering. 
Exposure to the air softens, and heating it to redness slightly 
hardens and whitens it. It is cracked by the same exposure. 
The rock is tough and difficult to break. It occurs in many 
large beds in St. Lawrence county in the township of Russell, 
New York. It is also distributed in smaller fields in Jefferson 
and Lewis counties. It accompanies the limestone and serpen¬ 
tines of that district, and may be readily distinguished from the 
latter by its hardness. In the absence of iron, chrome, chalce¬ 
dony, and the jaspery varieties of quartz, we may observe that 
it is unlike serpentine in its associations; still, as a mass, and 
in its position, it agrees with serpentine. It is not generally 
distributed in this country. 
Rensselaerite takes a very good polish, but less so than ser¬ 
pentine. Its texture and grain is even, and being easily 
wrought, especially that part of the rock which has been 
