C. Palache — Mineralogical Notes. 249 



Art. XXY. — Mineralogical Notes ; by Charles Palaohe. 



1. Zoisite Crystals from Chester, Mass. 



2. Pbenacite as an Alteration Product of Danalite 



from Gloucester, Mass. 



3. Crystal Form of Chalmersite. 



1. Zoisite Crystals from Chester, Mass. 



The crystals of zoisite here described were found some years 

 since by Mr. E. L. Cowles of Chester, to whom the writer is 

 much indebted for the generous loan and gift of material for 

 study and for information concerning its occurrence. 



Mr. Cowles states that the zoisite was obtained from " a vein 

 from two to five feet in width, located about three miles below 

 Chester," which is taken to mean down the valley of the West- 

 field River from Chester village. The locality is in the town 

 of Chester and is distinct from the well-known locality in 

 Huntington. 



The zoisite occurs in a rock consisting of a confused aggregate 

 of tremolite needles and prisms with colorless to pinkish diop- 

 side in stout prismatic crystals. In parts of the specimens 

 these minerals constitute the whole rock and again they are 

 cemented with granular calcite, suggesting that the rock as a 

 whole is a metamorphosed limestone. The zoisite is confined 

 to portions of the rock which appear to have once been open 

 cavities, into which the zoisite as well as tremolite and diopside 

 crystals projected. These cavities were afterwards infilled, 

 partly with quartz in which many of the crystals are imbedded, 

 partly with coarse granular calcite, removal of which with 

 dilute acid yielded the measured crystals. Irregular small 

 patches of lustreless granular graphite are also sparingly present 

 in the rock. 



The zoisite crystals are slender prisms up to 3 0ra in length 

 with lense-shaped cross section, the greatest diameter of which 

 is about l*5 cm . The prisms are deeply striated in the direction 

 of their length and commonly show a brilliant cleavage parallel 

 to the side pinacoid which truncates the thin edges of the len- 

 ticular prism section. They are white in color, transparent and 

 glassy in parts, but largely opaque and milk-white owing to the 

 presence of many flaws and cross- joints which traverse them 

 in various directions. 



Comparatively few of the crystals are terminated and only 

 one whose termination was complete was detached for 

 measurement. This crystal is shown in the figure* in about the 



*The figure was drawn and the table of angles compiled by Mr. H. E. 

 Merwin. 



Am. Jotjr. Sci. — Fourth Series, Vol. XXIV, No. 141. — September, 1907. 

 17 



