No. 2316. MINERALS FROM WESTFIELD, MASS.— SHANNON. 401 



tures have a thin layer of fibrous greenish-black material in which 

 as in similar material described by Emerson from Cheapside the 

 fibers are inclined at a small angle to the wall and appear as if combed 

 into position by movement along the fissure. At Deerfield such 

 fibers consist of diabantite and prehnite but at Westfield the fibers 

 are entirely calcite coated externally with diabantite with occasion- 

 ally a little interstitial stilpnomelane. Many small veins in the 

 upper quarries especially are lined with quartz crystals above which 

 is a layer of deep blackish to bluish-green submetallic stilpnomelane 

 in foliated small-micaceous or beautifully concentric botryoidal 

 surfaces. The series is closed by calcite which is easily separated 

 from the earlier minerals leaving fine broad surfaces of the stilp- 

 nomelane exposed. The visibly scaly or micaceous and botryoidal 

 forms are all, so far as tested, stilpnomelane, diabantite being in all 

 cases megascopically structureless. Botryoidal diabantite in amgda- 

 loid is described b}^ Emerson from Larrabee's quarry on the north 

 line of Holyoke. The writer visited this quarry but was unable to 

 find any specimens showing the chlorites in megascopic aggregates. 

 Well characterized stilpnomelane was found in quartz coated by 

 calcite at the quarry at the The Notch still farther north. 



Chlorophaeite which was found in the Deerfield trap at Cheapside 

 by Emerson was not observed at Westfield. The chlorophaeite, how- 

 ever, is an alteration product of an ea,rly generation of prehnite 

 which does not seem to be represented here. It is interesting at this 

 point to consider the similarity in composition between chlorophaeite 

 and stilpnomelane, the former being not unlike a greatly hydrated 

 and peroxidized variety of the latter. The stilpnomelane displays the 

 same tendency toward oxidation, in less marked degree, as is evi- 

 denced by its behavior in nitric acid and in its alteration as discussed 

 below. 



From time to tune specimens were found in the various quarries 

 which contained micaceous scales of a pure deep golden yellow color 

 and metallic luster. This was supposed to be the diabantite-vermicu- 

 iite of Emerson but none of the fragments exfoliated when heated. 

 In one place in the No. IV quarry this substance occurred in broad 

 surfaces of foliated and botryoidal aggregates of scales on quartz sur- 

 mounted by epidote prehnite and calcite. The superposed minerals 

 were easily separated from the golden coating which had exactly the 

 form and structure of the stilpnomelane of other parts of the quarry, 

 but appeared precisely as though coated with commercial gilt paint. 

 None of this material showed the characteristic exfoliation of a ver- 

 miculite. Though abundantly present this mineral was of exceed- 

 ingly small bulk, and it was found to be impossible to secure enough 



144382— 20— Proc.N.M.vol.57— 26 



