300 MINERALOGY. 



a more certain determination of the formula of several species and to 

 the discovery of very interesting A^arieties of old ones. Mr. Comstock 

 analyzed the tantalite, which occurs at Branchville, together with im- 

 mense crystals of the rare columbite, and also analyzed and fixed the 

 formula of urauinite, which before had never been found in such fine 

 and fresh crystals, and of which, therefore, no material so suitable for 

 analysis had been found. Mr. Penfield reached also as interesting re- 

 sults in his analyses of triphyllite and amblygonite, and also analyzed 

 a novel variety of apatite which was found to contain a large amount of 

 manganese. Profs. Brush and Dana have once more demonstrated the 

 economic value of scientific industry. Their new minerals were found in 

 a A^ery coarse-grained vein of pegmatite. They also found there immense 

 crystals of potash feldspar of the variety microcline, also masses of clear, 

 I^ure quartz. Having extracted many tons of these materials as waste 

 products in their search for the rare minerals, they took occasion to call 

 the attention of a ijorcelaiu manufacturer to it, and he found on trial 

 that the feldspar was eminently suited for the manufacture of his 

 wares, as was also the quartz. He therefore purchased the f)roperty, 

 and these materials have been systematically and extensively extracted 

 ever since. 



Profs. Brush and Dana have made another most imjiortant discovery, 

 fully equal in interest to their discovery of new species, since by means 

 of it they have perfected our knowledge of a species previously little 

 untierstood. The calcium borosilicate danburite was discovered many 

 years ago by Prof. C. XJ. Shepard, though its chemical composition was 

 subsequently first correctly determined by Profs. J. L. Smith and 

 Brush. Yet so small and imperfect were the grains then found that its 

 mode of crystallization was never known, or at least its form, could not 

 be correctly determined. It was thought to be triclinic. Through the 

 discovery of these gentlemen all the cabinets of the world are, or will be, 

 enriched with large and beautifully crystallized specimens of this hereto- 

 fore rare and insignificant species. The new locality is in Eussell, Ne\r 

 York, where danburite occurs in large, compact, rock-like masses and fine 

 crystals of perfect form. The little crystals are white and transparent, 

 and the large ones are also very perfectly formed. They are rhombic 

 in form, and, what is most remarkable, although it possesses no appar- 

 ent chemical affinity with topaz, its crystals are so deceptively like it 

 that no one would hesitate to pronounce it topaz from its outward ap- 

 pearance. This resemblance extends yet further; its axes are very 

 nearly identical in length, and its optical properties are nearly the 

 same as in topaz. Other cases of close resemblance in form between 

 unrelated chemical compounds are known. Calcite resembles soda nitre, 

 for example, and aragonite resembles saltpeter. Such resemblances of 

 the present time can only be explained as being the accidental resem- 

 blances, like those of faces in a crowd. But the fact that this borosilicate 

 resembles toj^az even in the minute details of arrangement of its crystal- 



