98 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



chromite, and chalcedony are surplus products of the serpentmous change. 

 Deweylite and picrosmine are, as it were, special vaiieties of the main pro- 

 duct, Avhile diaclasite, bastite, and "phsestine" (or marmolite) are derived 

 directly from enstatite. Of course remains of original calcite, dolomite, 

 magnesite, pyroxene, epidote, and olivine also appear. 



BLADED serpentine; ANTIO.ORITE- (OR BASTITE-) SERPENTINE. 



1. Serpentine tvlth dolomite. — Rowe, Massachusetts. Large bed at E. 

 King's, east of the tunnel, p. 79. Compact, even-grained, splintery fracture, 

 dark-gray, with trace of green on fractured or sawed surface, deep oil-green to 

 light apple-green on polished or wetted sui-face ; very translucent in splinters ; 

 abundant grains of i)}Tite and magnetite scattered through the mass. Dr. A. J 

 Hopkins detected chromium in small amount; for analysis, see p. 116. 



Slides show with pocket lens little magnetite, and preserve a uniform 

 pale-green color, even when ground extremely thin. 



Under the microscope is seen a network of interlaced serpentine blades 

 of unusual range in size, the smaller elongate, irregularly outlined as usual, 

 rhombic, and polarizing with bluish-white color; the larger broad, flat plates, 

 with straight, longitudinal cleavage lines, polarizing white of the first order 

 at border and deepening to yellow at center, the largest filling quarter of 

 the field (x 70) and deepening in color, through yellow to bright magenta. 

 These serpentine plates are sometimes arranged radially, showing a black 

 cross; at other times they are aiTanged apparently accoi'ding to the cleavage 

 of a former mineral, and are accompanied by black rod-like microlites in the 

 same direction. 



Another mineral, talc, appears in small veins and broad irregular 

 patches, as well as replacing to various depths certain laminae in the broad 

 bastite plates. It gives an aggregate polarization in bright, softly blended 

 colors, with wavy and sharp zigzag outlines. Leucoxene occurs, suiTound- 

 ing the black ore. Dolomite appears at times in regular rhombohedra, and 

 is generally in rounded grains, often with only faint traces of cleavage and 

 always without trace of twinning, 



3. Serpentine. — Chester. From the large Middlefield- Chester bed, at 

 brook-crossing on Chester road near the base of the mass. (See p. 81.) 

 Dull-black, with shade of brown; same color when wet; conchoidal fracture; 



