100 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



Under the mici'oscope very fine serpentine needles appear arranged 

 with a certain paralleHsm over bi'oad surfaces, a structure inherited from the 

 fohation; in some places they are larger, an-anged iiTegularly, and, being 

 thicker, show bright coloi's. 



Veins of chrysotile occur, with a certain portion of the transverse 

 needles replaced by magnetite. For analj-sis, see page 116. 



5. Serpentine nodule in talc. — Old emery mine, Chester. Light-gray with 

 shade of green; pale-green, translucent when wet; very fine-splintery frac- 

 ture, producing a whitish surface, as if dusted with fine grains. The slide 

 is pale-green, shows larg-e grains of iron ore, and bristles with magnetite dust 

 arranged along cleavage laminfe. Many spots of dolomite are visible with lens. 



Under the microscope it is seen to be made up wholly of a network of 

 fine sei-pentine blades, without any an-angement significant of the primary 

 mineral from which they were derived. 



6. Serpentine. — Chester. Another interesting sei'pentine occurs at the 

 emery mine. A pale apple-gi-een to oil-green rock, translucent, with shin- 

 ing luster, and haA-ing entu-ely the aspect of an indurated steatite; H = 2.5. 

 It breaks into thin, shaly fragments, bounded by wavy, slickensided sur- 

 faces, caused by pressure, and resembles deweylite. It has, however, 

 specific gravity 2.51, and under the microscope has the structure of a 

 platy sei-pentine and polanzes in white to yellow of the first order, and it is 

 decomposed by hydi'ochloric acid. 



The serpentines thus far described, with the exception of those from 

 the base of the large Middlefield bed, are characterized in greater or less 

 degree by the following peculiarities : 



(«) A harsh, splintery fracture. 



(6) Secondai'y magnetite wanting or unimportant, and where present 

 aiTanged often in long, wavy lines of the original lamination, as proved by 

 the cutting of slides at right angles to this lamination visible on weathered 

 surfaces of the I'ock. 



(f) As a consequence of (&), a gi-eat degree of translucency in the 

 rock when wet or polished, while the succeeding enstatite-serpentines are 

 very genei'ally black and opaque when moistened. 



(f/) The mass of the rock is made up of distinctly polarizing sei^pentine 

 (antigorite) in bladed crystals, which stand in relation to the spliuterv 

 fracture; and there is lack, at least nearly complete, of an amor})hous 

 serpentine substance and of cluysotile. 



