66 natural history. (Minerals.) [north 
result of smelting of which the more remarkable, on account of its 
locality, is that cast in the form of thick wires, brought by Capt. Clap- 
perton from Soudan in Africa, and mentioned in the Appendix to his 
Journal). 
In the next Case begin the oxides of electro-negative bodies, and 
their various combinations. 
Case 19. Alumina and Aluminates. To the former belongs the 
corundum or corundite , divided into noble and common corundite, the 
former 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;—the latter, to which the name of corundum 
is more especially applied, affords one of the hardest and best polishing 
materials to the lapidary: from Bengal, Mysore, China, the Carnatic 
(Werner’s diamond spar), New Jersey, Lapland, Piedmont, &c. As 
appendix to these are added, the emery , a compound substance which 
derives its hardness and consequent usefulness for polishing to blue 
or grey corundum ; and the indianite of Bournon, which sometimes oc¬ 
curs as matrix of the common corundum of the Carnatic. As hydrates 
of alumina are to be particularized, the diaspore from the Ural, and 
the hydrargillite of G. Rose : the latter a mineral from Shimshimskaja 
Gora, which is to be considered as crystallized gibbsite , if Torrey’s 
analysis of the latter be correct; but as, according to Hermann, the 
gibbsite contains upwards of 37 p. c. of phosphoric acid, it is at present 
placed with the phosphates (Tab. 57): the mineral called wavellite of 
Villaricca, being no phosphate, is now referred to the hydrargillite, with 
which it agrees in its chemical composition. 
The aluminates of magnesia :—the spinel , among the principal va¬ 
rieties of which, besides the red and violet, may be specified the blue 
spinel of Aker in Siidermannia, to which is related the sapphirine ; the 
brown, often found in crystals of considerable dimension, from New 
Jersey; and the chlorospinel of Rose, in which a portion of the alumina is 
replaced by oxide of iron, from Slatoust, Siberia;— the sapphirine, &c.; 
—the ceylonite or pleonaste, and the automolite (also called gahnite ), 
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 chrysoberyl or cymophane , considered as an alu¬ 
minate of glucine and of iron, among the specimens of w T hich deserve 
particular mention the large crystals from Brazil and from the Ural, 
(the latter green variety, but of a columbine red by transmitted light, 
has been called alexandrite ); those in a matrix of quartz and feldspar 
with garnets, from Haddam in Connecticut, and also those from Sa¬ 
ratoga and New York.—The mineral called gum-lead (plomb gomme), 
which occurs at Huelgoet in Brittany only, is essentially a hydrous 
aluminate of lead. 
The five following Cases contain the acid or oxide of silicium (silica), 
the numerous varieties of which, formerly considered as so many 
distinct species, are mostly indebted for their generally very striking 
external characters to the admixture of matter foreign to the species, 
or to other casual circumstances that prevailed at their formation. 
Case 20. Amethyst quartz of various tints, in grouped crystals, &c. 
.Rock crystal: various modifications of crystalline forms; small 
