MINERALOGY, 113 
72. Tarc [H? Mg? Sit O”]. 
Talc, as it occurs in New Hampshire, is chiefly of the variety called 
steatite, or soapstone, of which we have large beds that have been exten- 
sively worked. At Francestown there is a large quarry where talc of ex- 
ceptional purity has been mined since 1802. At Orford there are five 
beds, but the mineral is of a slaty character, and not so easily worked. 
At Richmond the beds are still more impure, and the mineral con- 
tains anthophyllite and pyrites, which interfere with the sawing of it 
into blocks. Keene, Weare, Warner, Canterbury, and Lancaster are 
other localities where steatite has been found. The impure varieties 
are of economic value, though they may not be transported to markets 
at adistance. At Haverhill a large bed of steatite was long ago found, 
and very large boulders of soapstone are found at Pelham, which have 
been transported from some unknown locality. At Norwich Vt., the 
pretty green foliated variety of talc has been found. 
Talc is not found with well formed crystal faces, but it is considered 
orthorhombic, and its microscopic characters correspond to those of such 
crystals. The steatite in thin sections appears to be a fibrous mass, and 
where the fibres do not overlie one another so as to interfere with one 
another, the fibres are dark when parallel to the plane of vibration of the 
light. If we take one of the folize of the nice green talc from Norwich, 
and put it under the microscope, take out the ocular and cross the Nicols, 
we shall see a black cross which opens out into two hyperbolas as the 
section is revolved, and which shows the biaxial character of the crystal, 
and that the optic axial angle is not large (17°-19° in the air). These 
characters agree with those belonging to talc, in which the cleavage is 
basal, the bisectrix normal to the base, and the optic axes in the plane of 
the macrodiagonal. 
Tale is a constituent of some of our rocks. In thin sections of them 
it is usually in radiated masses. It is distinguished from chlorite in that 
it shows neither dichroism nor absorption of light, and is usually fresh 
and undecomposed. 
Tale enters into some granitic rocks, forming protogene, and with 
some accessories forms the stratified talc schist. Much of the so-called 
talcoid schist of Vermont and New Hampshire was shown by Prof. G. F. 
VOL. IV. 15 
