WARREN AND PALACHE. — QUINCY PEGMATITES. 163 



o> ray is bright yellow, often with a brownish tone ; the e ray is golden 

 yellow. The absorption is w > c slight. For crystals 1 mm. thick the 

 dichroism and absorption is but slightly greater. Upon alteration the 

 crystals become filled with a dusty product, are less transparent, and 

 often exhibit a brownish or brownish-red stain of varying intensity. 



The indices of refraction were determined by the immersion method 

 using a barium-mercuric-iodide solution. The determinations were 

 made on a number of perfectly clear, small crystals chosen on account 

 of the uniform development of their prism zones ; also upon one larger 

 crystal (l^mm. in diam.) terminated by a perfect basal plane which 

 made it possible to orientate the crystal and cut a section parallel to 

 the prismatic axis. An attempt was made to measure the indices 

 directly upon this crystal by means of the Abbe refractometer but with- 

 out success owing to the small size of the section and its low degree of 

 transparency. The fine striations parallel to the edge between the 

 base and the prism stand out very sharply under the microscope and 

 make it possible to orientate the crystals with great accuracy on the 

 microscope stage. The values obtained with sodium light are given 

 below, also those heretofore given for parisite as determined by 

 Senarmont and those for synchisite according to Flink. 



The Montana parisite, also crystals from Muso valley taken from the 

 mineral collection of Harvard University were tested by the immersion 

 method and their indices were found to correspond to the values given 

 for the Quincy mineral. The older values given for the Muso mineral 

 appear to be quite wrong. The ordinary rays for parisite and synchi- 

 site are almost identical. The extraordinary rays appear to differ by 

 0.0131. While the extraordinary ray for the Quincy mineral is prob- 

 ably not as accurately determined as the value for the ordinary, 

 the error can hardly be as great as 0.0131, and the difference between 

 the two minerals for this constant may be a real one. 



Chemical Composition of Parisite. — About a kilo of fine-grained 

 material recovered from the fragile lining of the central pockets was 

 carefully washed and fractioned by means of screens, an electro magnet, 

 and heavy solutions until a fraction was obtained weighing about ten 

 grams and consisting largely of parisite mixed with more or less aegirite, 

 octahedrite, feldspar, and quartz. From this about three grams of clear 



