Prof. Maskelyne and Dr. Lang's Mineralogical Notes. 445 



racters of which we are indebted to the refined optical inves- 

 tigations of M. Des Cloiseaux. 



The spherules appear in different aspects under the microscope : 

 greenish-brown wax-like nodules with a laminar structure are 

 frequent among them, while others exhibit a more decidedly 

 crystalline appearance. In section these nodules present the cha- 

 racters (and the probably prismatic system) of what for the pre- 

 sent we may call the fanned mineral — grey in tint from an 

 infinitesimal dust of iron and other foreign matter chiefly accu- 

 mulated between the laminae ; and they seem to pass by differ- 

 ent stages into a mottled mineral (or minerals) which, from a 

 confusedly crystalline structure, acts on polarized light as agate 

 does. This mottled form of mineral in particular cases may be 

 seen to consist of the fanned or the barred mineral seen in a 

 section cut across the fibre, so to say, of the prisms, and pre- 

 senting therefore a vast number of sections of these in confused 

 arrangement. It would be an arduous task, and take a large 

 amount of material, to pick out enough of the several varieties 

 of these nodules from the bruised fragments of an aerolite to 

 furnish a sufficient quantity for a trustworthy analysis. But the 

 fanned and mottled minerals are among the very few the 

 spherules of which might perhaps be so treated in this class of 

 aerolites. Some of the spherules exhibit a quasi-crystalline 

 exterior, and these are generally such as consist of crystals, and 

 in Nellore generally of one imperfect individual crystal, usually 

 surrounded by a fringe of irregularly disposed and minute cry- 

 stalline fragments ; while in other aerolites (as in Aussun for 

 instance) we find such spherules often to contain perhaps four 

 or five largish and well-defined crystals with a number of minuter 

 ones interspersed between them. But the planes of polarization, 

 and therefore the orientation, of each crystal seem quite inde- 

 pendent of those of the rest, and the apparent crystalline out- 

 line of the spherules seem seldom in these cases significative of 

 an internal crystallographic structure. 



The singular observation of the natives, that the Nellore stone 

 was white when it fell, may be accounted for on the suppo- 

 sition that it has acquired its rusty stains since. This rusty 

 character, so obvious a feature of the aerolites of Mainz, Char- 

 wallas, and Segowlee, and in a less degree of Nellore among 

 others, is certainly the result of oxidation since their fall. The 

 difficulty of taking the specific gravity of an aerolite illustrates 

 its porosity. Even the most compact aerolites absorb much 

 water in that process. In the microscope the stains of ferric 

 oxide are seen surrounding the larger granules of metallic iron, 

 curiously distinguishing them from the meteoric pyrites; but 



Phil. Mag. S. 4. Vol. 25. No. 170. June 1863. 2 II 



