12 



PROCEEDINGS OF THE ACADEMY OP 



[1889. 



The filtrate from B, after CaC 2 0' had been removed, was evapo- 

 porated, and residuum ignited. It yielded a sodium reaction, but not 

 sufficient to account for the lack of three per cent in the analyses. 

 Iron was found in very small quantity. 

 The pigment appears to be a carbon compound. 

 Pyrite is visible in several places surrounding the anhydrite. 

 A thin section of the rock showed essentially an emerald green 

 mineral (black when thick) which polarized very weakly and showed 

 little dichroism. With it a white, very transparent mineral, which 

 polarizes like a plagioclase. Besides these only small grains of a 

 bluish purple mineral could ba seen. It was possible to separate, 

 by Mercuric iodide, the white mineral in a pure state. 

 Its analysis, made with - 20 gr. gave 



CaO = 0-0228 (diff.) SiO 2 = 55-88 



APO 3 = 0-0568 (white) * APO = 28-40 

 Na'SO 4 = 00210 CaO = 11-14 



Na 2 = 4-58. 



100-00 

 The plagioclase is therefore Labradorite. 



The green mineral could not be freed either from the plagioclase 

 nor from the dark brown grains. The analysis gave 



SiO 2 

 APO 3 

 CaO 

 Na 2 



= 10-92 

 = 5-55 



= 2-15 

 = 0-92 



• Labradorite 



Pyroxene 



SiO 2 =36-531 



APO 3 1-85 



FeO = 12-08 

 100-00 CaO =19-78 



MgO = 9.75 

 Ignition = 0'47 y 

 That the green mineral must betaken as a Pyroxene follows from 

 its optical behavior and also from the fact that the splinters show 

 under the microscope a nearly rectangular cleavage. The nature 

 of the roundish brown grains could not be ascertained. 



We have here the existence of anhydrite as a secondary crystalli- 

 zation on an undoubtedly intrusive rock. It's elements are to 

 be found in the calcium of Labradorite and Pyroxene, and the sul- 

 phur of the Pyrite. But one should expect to see Selenite crystal- 

 lizing under these conditions. Some years ago (Proc. Acad. 1873,) 

 the author showed how anhydrite tails from a solution of calcium 

 sulphate at 150°C. in a sealed tube, but selenite at the boiling point at 

 atmospheric pressure. The existence of high pressure with or without 

 heat would account therefore for the anhydrite on Diabase. The 

 author is not aware that this mineral has heretofore been found 

 among the epigenetic products of crystalline intrusive rocks. 



