No. 2316. MINERALS FROM WESTPIELD, MASS.— SHANNON. 



399 



analyses differ slightly from those of Hawes on Farmington material 

 they are sufficiently close that the material may be referred to 

 diabantite without question. The results of tlie analyses are tabu- 

 lated below: 



Analyses of diabantite. 



Constituents. 



SiO 



AI2O3 



FeA 



FeO 



MgO 



CaO 



MnO 



H2O-105°C 

 H2O+105°C 



Total. 



28.12 



15.93 



3.99 



25.09 



14.48 



.78 



.17 



.40 



11.02 



99.98 



27.90 



16.13 



3.85 



25.22 



14.67 



.53 



.17 



.63 



11.41 



100. 51 



28.50 



14.39 



3.91 



25.28 



14.35 



.56 



.27 



.64 



11.13 



99.03 



28.09 



14. 23 



3.64 



25.31 



14.74 



.50 



.23 



.62 



11.44 



98.80 



28.15 



15.17 



3.85 



25. 23 



14.56 



.59 



.21 



.57 



11.25 



99.58 



Some time after the above analyses had been completed, there 

 was found, on the face of the No. 4 quarry, a similar vein containing 

 abundant clayey green material. This vein was not marked by 

 any such pronounced alteration of the walls and its first lining was a 

 crystal crust made up of calcite in peculiar trigonal crystals formed 

 by half of an obtuse rhombohedron truncated by a bright basal 

 plane. Over and around these crystals was the thick layer of clay 

 which varied in color from bright verdigris to olive green. Last 

 here as before came calcite in broad translucent cleavage masses 

 containing cavities lined with nearly cubic rhombohedrons of calcite. 

 This being the second occurrence of fine homogeneous material 

 suited for chemical investigation, which was found, its examination 

 was undertaken in order to determine whether it conformed more 

 closely than did the previous lot to the diabantite of Hawes. Sur- 

 prisingly enough, this material was found to be entirely unlike 

 diabantite in composition and to be quite clearly referable to stilp- 

 nomelane. The structure is in places somewhat platy as though 

 pseudomorphous after some platy mineral or as though it had been 

 deposited between the plates of some mineral now entirely removed. 

 In color it is more bluish than the diabantite, the clayey variety is 

 more plastic, when micaceous it is apparently more opaque and 

 there is a peculiarly submetallic luster, which is wanting in diaban- 

 tite. In drying these specimens do not develop many slu-inkage 

 cracks and the dried material instead of being soft and friable is so 

 compact and tough that it is difficult to pulverize in a mortar. 

 Under the microscope this mineral, like the diabantite, is seen to 

 consist of micaceous scales, imperfectly transparent and pleochroic 

 in tones of light to dark brownish-green. Basal plates are dark 



