1895. PROCEEDINGS OF THE NATIONAL MUSEUM. 285 



again in the form of compact bundles of flat fibers of a grayish hue, 

 several inches in length. The larger bundles found at this locality fre- 

 quently show rude cross i)artings, indicative of a rupturing through 

 shearing agencies, the clefts thus formed being filled by other second- 

 ary minerals. The significance of this fact is noted later. The mate- 

 rial from Idaho (Analysis 32) can scarcely be considered a true mineral 

 species, being partially decon^posed by cold dilute hydrochloric acid, 

 the solution reacting for alumina and magnesia, while the insoluble resi- 

 due consists of pure white, brittle fibers, in the form of fiat bundles, show- 

 ing to the naked eye a peculiar crimping extending diagonally across 

 the plates. The two samples from Nahant and Maiden, Massachusetts, 

 received from Prof. W. O. Crosby, occur in diabase, the fibers running 

 oblique or parallel with the walls of the "vein.'' That from JS^ahant 

 is a dull, light-green gray, platy mineral, shredding up readily into flat- 

 tened bundles of fibers which lie with their greatest diameters in one 

 general plane. The fibers, under the microscope, are very uneven in 

 diameter and splinterlike, terminating in acute points. There seems 

 almost no limit to fibration, bundles not over 0.004 mm. in diameter 

 being made up of a large number of short, splinterlike fibers, with 

 free ends frequently projecting like the broken strands in an old rope. 

 Fibers were measured down to 0.001 mm. in diameter, but smaller exist. 

 Small flattened fibers, the fraction of a millimeter in diameter, give 

 extinction angles, measured against the edge, of 7°, and show indis- 

 tinctly the emergence of a bisectrix a little to one side, facts at once 

 suggestive of cleavage splinters parallel to the prismatic faces. Meas- 

 urements on a number of small individual fibers show extinction angles 

 ranging from 0'^ to 17°. The Maiden material is very similar, but the 

 fibers are longer and more uniform in diameter. The composition and 

 optical properties of both are such as to relegate them to the "uralites" 

 rather than to true asbestos, though their fibrous structure is none the 

 less suggestive from our present standpoint. 



A platy, dull greenish, soft, and rather brittle mineral found at Kox- 

 bury, Massachusetts, under similar coiulitions, shows under the micro- 

 scope stout, faintly yellowish, and pleochroic columns, with frequent 

 cross partings which give extinction angles as high as 22". The material 

 is doubtless actinolite, and was not analyzed. 



Concerning the possible cause of tlie fibrous structure ot these min- 

 erals, existing literature is strangely silent, though there are numerous 

 references to the occurrence of asbestos as a secondary mineral. Thus 

 Blum describes' the conversion ("umwandlung") of an augite from 

 Pitkaranda, in tlie Ladoga-See, into an asbestos-like hornblende, the 

 process being evidently akin to uralitization. He finds also a fibrous 

 intermediate product having the following composition: SiO^, 45.57 per 

 cent; ALO;, o.OO percent; FeaOr;, 19.73 per cent; CaO, 4.40 ])er cent; 

 MgO, 23.40 per cent; H20, 2.00 per cent. In the angites from the Brozza- 



' Die Psendomor])li()sen des Jlineralreiches, 18415. 



