109 
of radiated-fibrous small globules, and marked with 
concentrically disposed brown and yellow colours, is 
called toad’s eye wood-tin. 
In the next glass case begin the oxides of electro¬ 
negative bodies, and their various combinations. 
Case 19. Alumina and Aluminates . To the former 
belongs the corundum , comprehending the precious 
stones, commonly called oriental gems, (the sapphire, 
ruby, oriental amethyst, oriental topaz, oriental emerald,) 
of the crystallized forms of which the principal modifi¬ 
cations are here deposited ; and the common or imper¬ 
fect corundum from Bengal, Mysore, China, (Werner’s 
diamond spar,) Lapland, Piedmont, &c. As appendix 
to these are added, the Jibrolite (bournonite of Lucas,) 
one of the concomitant substances of the common corun¬ 
dum ; and the emery , which owes its hardness and con¬ 
sequent usefulness in polishing to an admixture of blue 
corundum.— The diaspore and th egibsite: both hydrates 
of alumina.— Aluminates of magnesia —the spinel: 
o 
among its varieties is the blue spinel of Aker in Siider- 
mannia. The ceylonite or pleonaste, and the automo- 
lite from Fahlun in Sweden and from Franklin in New 
Jersey, are, the former an aluminate of protoxide of 
iron and magnesia, the latter an aluminate of zinc.— 
The substance called plomb gomme , from Huelgoet in 
Britanny : a hydrous aluminate of lead. 
The five following glass cases contain silica or quartz, 
the numerous varieties of which, formerly considered 
as so many distinct species, are mostly indebted for their 
generally very striking external characters to the ad¬ 
mixture of matter foreign to the species, or to other 
casual circumstances that prevailed at their formation. 
Case £0. Rock crystal: various modifications of 
crystalline forms : small dodecahedral and other crys¬ 
tals, known by the names of Gibraltar diamonds, Bristol 
diamonds, &c.; varieties of colour according to which 
the substance obtains the familiar denominations of 
smoky topaz or morion, cairngorm, citrine, &c.; speci¬ 
mens of rock crystal, enclosing various substances, such 
LONG 
GALLERY. 
Nat. Hist. 
as 
