GALLERY.] NATURAL HISTORY. 105 
agate veins, and the porcelain jasper, produced by the action 
of subterraneous fire on clay slate. The other half of this 
Case contains opaline substances (mostly hydrates of silica), 
viz., specimens of the noble opal , which owes its beautiful 
play of colours to a multiplicity of imperceptible fissures in 
its interior;—the sun ox fire opal ;—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 which, having the pro¬ 
perty of becoming transparent when immersed in water, is 
called hydrophane, and vulgarly, oculus mundi;— wood 
opal, or opalized wood;— jasp-opal, referred by some 
authors to jasper;—the menilite, called also liver opal, 
found at Menil-Montant, near Paris, in a bed of adhesive 
slate, a specimen of which is added. 
In the two next Cases are placed the Silicates with one 
base. 
Case 25 contains the silicates of lime and those of mag¬ 
nesia. To the former belongs the table spar or wollasto- 
nite from Mount Vesuvius, Nagyag, &c.;—to the latter, 
several of the minerals placed by Werner in the talc genus: 
— steatite , the more remarkable varieties of which are, that 
of yellowish green colour from Greenland, and that from 
Gopfersgriin in Bareuth, with small crystals of other mine¬ 
ral substances, especially quartz, converted into, and form¬ 
ing part of the massive steatite; variety called chalk of 
Brian^on;— 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 keffe- 
killite by Dr. Fischer, who discovered it in the Crimea;— 
liihomarge , the more remarkable varieties of which are, 
that of a reddish yellow colour in porphyry from Kochlitz, 
and the fine purplish blue variety from Planitz, formerly 
called terra miraculosa Saxonica, &c.— serpentine, the purer 
varieties of which (generally hydrates) are called noble 
serpentine: they constitute, in combination with primitive 
limestone, the verde antico and some other fine green mar¬ 
bles ; among the varieties of the common serpentine, those 
from Bareuth and from Zoblitz in Saxony are best known, 
where they are manufactured into vases and various other 
articles; serpentine with imbedded garnets, magnetic iron- 
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