1873.] ^i'J [Genth. 



"corundum resembling emery in its physical characters, but the presence of 

 grains of corundum in the liydrated mineral seems to shoio that the trans- 

 " formation may take place at ordinary temperature." I do not know of 

 a single instance, in which corundum could have been eliminated under 

 such circumstances from the hydrate ; on the contrary, the presence of 

 grains of corundum in the beauxite prove pretty conclusively, that the 

 latter results from the hydration of corundum, and that the grains which 

 have been found are remnants not yet converted. The same may be said 

 of the inclosing argillaceous matter, that it is the result of the alteration 

 of corundum. 



5. Gibbsite. 



This very rare hydrate of alumina has been so far as I can discover, 

 only twice noticed in contact with corundum, evidently resulting from 

 its hydration, first at Gumuch Dagh, Asia Minor, by J. L. Smith (loc 

 cit.) who observed it as forming an external coating of a crystal of 

 corundum, and also in the form of a hexagonal prism. The latter is very 

 probably a pseudomorph of gibbsite after corundum. The second locality 

 is at Unionville, Pa., where T. F. Seal* found it as a thin coating of small 

 mamillary incrustations on the albite rock. (The other coatings on 

 corundum crystals, of which he speaks, are evidently not gibbsite, but 

 margarite, as I shall show in the sequel.) 



G. Quartz. 

 Sillemf mentions that quartz occurs pseudomorphous after corundum. 

 I have never observed this pseudomorph, and have not seen the origi- 

 nal paper, I therefore merely mention the fact for the sake of complete- 

 ness. 



7. Opal. 



It is perhaps worthy of notice that I have observed the variety hyalite 

 in connection with corundnm and minerals resulting from its alteration. 

 At the Culsagee Mine it is rarely found in beautiful colorless and white 

 botryoidal incrustation upon foliated chlorite, and also upon corundum. 

 From Dudleyville, Alabama, I have one specimen, on which it occurs as 

 a brownish-white botryoidal incrustation upon blue cleavable corundum. 



One of the pseudomorphous fibrolite crystals, from Mineral Hill, Dela- 

 ware County, Pa., has a slight coating of an amorphous botryoidal 

 vitreous mineral, which appears to be hyalite. 



8. Smaragdite (?) (Kokscharopfite). 



I have already mentioned the peculiar rock formed by Smaragdite (?), a 

 feldspathic mineral, and grains of pink or even deep ruby corundum, and 

 sometimes chromite disseminated through the mass, which occurs at the 

 Cullakenee Mine. 



The grains of smaragdite (?) are very indistinct in form, but frequently 

 show an obtuse angle like that of an amphibole. The color is from 



*T. F . Seal. Sill. Journ. [2] xi. 267. 



tSillem, Leonhard & Bronu's Jahrbuch — 1S5] , 3S5. 



