NATURAL HISTORY. 
53 
GALLERY.] 
Case 19. Alumina and Aluminates. To the former belongs the 
corundite, divided into noble and common corundite, the former com¬ 
prehending the precious stones commonly called oriental gems (the 
sapphire, ruby, oriental amethyst, oriental topaz, oriental emerald), of 
the crystallized forms of which the principal modifications are here 
deposited; the latter, to which the name of corundum is more espe¬ 
cially applied, affords one of the hardest and best polishing materials 
to the lapidary; from Bengal, Mysore, China, the Carnatic (Werner’s 
diamond spar), Lapland, Piedmont, &c. As appendix to these are 
added, the emery, a substance which derives its hardness and consequent 
usefulness for polishing to an admixture of blue or grey corundum ; 
and the indianite of Bournon, which som.etimes occurs as matrix of the 
common corundum of the Carnatic. 
As hydrates of alumina are to be particularized, the diaspore from the 
Ural, and the gibhsite from Massachusetts, and the hydrargillite of Rose, 
(not of Davy,) from Lissensko, in the Shisshimskian mountains. 
Aluminate of magnesia—\hQ spinel: ^ among its principal varieties 
may be specified the blue spinel of Aker in Siidermannia, and the 
browm, often in crystals of considerable dimension, from New Jersey; 
—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 chrysohenjl or cymophane, considered as an alu¬ 
minate of glucine and of iron, among the specimens of which may be 
specified the large crystals from the Ural and from Brazil, those in a 
matrix of quartz and feldspar with garnets, from Haddam in Connec¬ 
ticut, and also those from Saratoga and New York;—the mineral called 
gum-lead {plomh gomme), which occurs at Huelgoet in Brittany only, 
and is a hydrous aluminate of lead. 
The five following Cases contain the acid or oxide of silicium (silica), 
the numerous varieties of w’hich, 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 ccisual circumstances that prevailed at their formation. 
Case 20. Amethyst quartz of various tfnts, in grouped crystals, &c. 
—Rock crystal: various modifications of crystalline forms: small 
dodecahedral and other crystals, known by the names of Gibraltar 
diamonds, Bristol diamonds, &c. ; varieties of colour, according to 
which this substance obtains the familiar denominations of smoky topaz 
or morion, cairngorm, citrine, &c. ; specimens of rock crystal enclosing 
various substances, such as rutile, brown iron-stone, micaceous iron, 
acicular antimony, actinote, asbest, chlorite, 8cc.; groups of rock 
crystal; some specimens of rock crystal in a wrought state are added, 
among which is Dr. Dee’s show-stone (see Walter Scott’s Demono¬ 
logy), &c. 
Case 21. Common quartz: among the specimens of this widely 
diffused substance, which offers such a great variety in its external 
aspect, the more remarkable are the hacked, corroded, and cellular 
quartz from Scheranitz, as also the pseudomorphous or supposititious 
crystals, principally derived from modifications of calcareous and fiuor 
spars; and, with regard to colour, the blue quartz, called siderite, from 
Salzburg, and the rose or milk quartz, v;hich are both used as ornamental 
stones;— fibrous quartzflexible sandstone (itacolumite) from Brazil, 
