CONTRIBUTIONS FROM THE MINERALOGIC LABORATORY IQ 

 SUMMARY OF MEASURED AND CALCULATED ANGLES 



DATOLITE FROM WESTFIELD MASS. 



In February 1905 the State Museum acquired by exchange 

 from Mr R. F. Jones a number of specimens of datolite from Lane's 

 trap quarry near Westfield Mass. As the quality of this occurrence 

 far exceeds that of the datolite hitherto described from this region, 

 in size, beauty and complexity of crystallization, the writer has 

 added the following notes to the foregoing descriptions of New 

 York minerals in the hope that the unusual interest attached to 

 these crystals will prove sufficient excuse for such an extralimital 

 digression. 



The datolite occurs in veins in a diabase which shows evidence 

 of considerable folding and decomposition, particularly along the 

 walls of the vein where it is entirely replaced by prochlorite. The 

 crystals which in some instances measure 10 cm. on the b axis 

 are deposited on a thin layer of calcite. They are cut through by 

 deep parallel furrows due to the former presence of mica which 

 has been dissolved away leaving the cast, partly filled with calcite 

 of a later generation; fragments of this mica, highly altered, were 

 found in place. In color the crystals are whiter than those from 

 the New Jersey trap region which they strongly resemble in crystal 

 habit. The presence of second generation calcite of the form / 

 (0221), which also occurs associated with the datolite from West 

 Paterson, gives added significance to this similarity. The faces 



