52 
natural history. (Minerals.) 
[north 
veins, and the 'porcelain jasper, produced by the action of subterraneous 
fire on clay-slate. The other half of this Case contains opaline sub¬ 
stances (some of them hydrates of silica), viz., specimens of the noble opal , 
which owes its beautiful play of colours to a multiplicity of otherwise 
imperceptible fissures in its interior ;—the sun-opal , or fire-opal , ex¬ 
hibiting a suite of colours, from deep orange yellow to nearly untinged; 
found in the trachytic porphyry of Zimapan, in Mexico;—the common 
opal , a translucent white variety of which, appearing yellow or red 
when held between the eye and the light, is called girasol;—the semi¬ 
opal, agreeing in its principal characters with the common;—specimens 
of a variety both of common and noble opal, which, having the property 
of becoming transparent when immersed in water, is called hydrophane, 
or oculus mundi;— wood-opal , or opalized wood, chiefly from Hungary ; 
— jasp-opal, referred by some authors to jasper;—the menilite, or liver 
opal, found at Menil-le-Montant, near Paris, in a bed of adhesive slate, 
a specimen of which is added;—the red opaline substance called 
quincite , from St. Quintin and from Mehun in the Department de 
Cher, is common opal tinted, as it is supposed, by organic colouring 
matter, in the same manner as the magnesite occurring with it in the 
fresh water limestone of that part of France. 
In the two next Cases are placed the Silicates with one base. 
Case 2 5 contains the silicates of lime and some of the silicates of 
magnesia and of alumina. To the former belong the table spar or 
wollastonite from Mount Vesuvius, Nagvag, &c., and the okenite; 
perhaps also the alumocalcite of Breithaupt, before considered as de¬ 
composed opal, from Eibenstock, Saxony. 
The silicates of magnesia comprehend several of the minerals placed 
by Werner in his talc genus:— steatite , or soapstone, the more interest¬ 
ing varieties of which are, that of yellowish green colour from Greenland, 
and that from Gdpfersgriin in Franconia, with small crystals of other 
mineral substances, especially quartz, converted into, and forming part 
of the massive steatite ; variety called chalk of Briancon;— keffekil, or 
meerschaum, from Natolia, of which the well-known pipe-bowls are 
made, and that from Valecas in Spain ;—also a related substance, 
called kejfekillite by Dr. Fischer, who discovered it in the Crimea;— 
the lithomarge , or steinmarh, has been associated with steatite, although 
most of its varieties are silicates of alumina: the more remarkable of 
wdiich are, that of a reddish-yellow colour in porphyry, from Rochlitz, 
and the fine purplish-blue variety from Planitz ( teratolite , formerly 
called terra miraculosa Saxonica), &c.— serpentine, the purer varieties of 
which (generally hydrates) are called noble serpentine : they constitute, 
in combination with primitive lime-stone, the verde antico and some 
other fine green marbles; crystallized serpentine, from Snarum, in Nor¬ 
way ; — among the varieties of the common serpentine, those best known 
are from Baireuth and from Zoblitz in Saxony, where they are manu¬ 
factured into vases and various other articles: serpentine with embedded 
garnets, magnetic iron-stone, asbest, &c..— Of other substances nearly 
related to serpentine in this Table Case we have, the hydrophite of 
Svanbero;;the picrolite; the antigorite; the villarsite, &c.—With these 
are also placed the metalloid diallage or diallagite, more commonly called 
schiller-spar, from the Hartz, &c.; and some varieties of what is called 
bronzite and xanthophyllite _To the silicates of magnesia is also re¬ 
ferred the olivine , a green granular substance, occurring chiefly in trapp 
