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many respects. It is about one quarter of an inch in diameter, 

 and of a spherical shape. Its surface, evidently a natural one, 

 is smooth, and of a milk-white color, witli little lustre. On close 

 examination, the surface appears mottled, and faint undulated 

 markings are seen within. In hardness it much exceeds true 

 pearls, equalling feldspar, or the average hardness of opal. The 

 hardness of pearls varies to some extent. Several specimens of 

 dirt'erent sjjecies which I had an opportunity to test ranged be- 

 tween calcite and fluor-spar ; none were so hard as fluor. 



Chemical composition. The cocoa-nut pearl consists of car- 

 bonate of lime, w'ith a very small proportion of orgaiiic matter ; 

 so little that it does not blacken nor evolve any odoj- before the 

 blowpipe. When the carbonate of lime is removed by the slow 

 action of very dilute acids, a transparent substance remains, of 

 great tenuity, showing no structure under the microscope, and 

 incapable of preserving its form. Notwithstanding the filmy 

 character of the organic residue, a few micro-chemical reactions 

 were satisfactorily obtained. It is insoluble in water, alcohol, 

 and ether. With strong nitric acid it takes a yellow color, and 

 on adding ammonia becomes intensely yellow. Iodine colors it 

 brownish yellow, and the addition of concentrated sulphuric acid 

 does not change the color to blue, the tint given by iodine be- 

 ing retained a week or more. These reactions are sufficient to 

 indicate that the organic substance is an albuminous body, and 

 not cellulose, the basis of vegetable tissues in general. Since 

 albuminous substances occur in plants as well as in the animal 

 kingdom, we cannot from these reactions infer the animal ori<nii 

 of the gem in question. True pearls consist of carbonate of lime, 

 with a considerable amount of albuminous animal matter. When 

 decalcified by dilute acids, the organic residue retains the form 

 and structure of the j^earl ; and in the nacreous pearls, the charac- 

 teristic iridescence also. 



Microscopical characters. Thin sections examined under the 

 microscope show that the cocoa-nut pearl is composed of numer- 

 ous regularly concentric lamince, adhering pretty firmly together. 

 These layers form groups differing slightly in tint, and near the 

 exterior are often exceedingly thin. The centre is occupied by 

 a semitransparent mass resembling the surrounding layers. No 

 foreign nucleus was found. The general mass is made up of radi- 



