NATURAL HISTORY. 
[north 
54 
mocha-stones; varieties with white, .brown, and black, straight or 
curved lines, some of which were probably among the substances of 
which the costly vasa murrhina of the ancients were made; red and 
yellowish varieties of calcedonv called carnelian — Plasma — Heliotrope, 
an intimate mixture of calcedony and green earth, which, when con¬ 
taining disseminated particles of red jasper, is commonly termed blood¬ 
stone.—The beautiful and much esteemed variety of calcedony called 
chrysoprase, hitherto only found at Kosemiitz in Silesia, and which 
owes its colour to oxide of nickel, as does the green siliceous earthy 
substance, named pimelite, which accompanies it. To these are added 
specimens of some varieties of the siliceous compounds called agates , 
in which common calcedony, carnelian, and heliotrope generally form 
the predominant ingredient. 
Case 24. One half of this Case is occupied by the different 
varieties of jasper, such as they are enumerated by Werner, viz. the 
globular or Egyptian jasper, found chiefly near Cairo, in rounded 
pieces, which do not owe their form to rolling, but are, according to 
the opinion of some writers, produced by infiltration, or, what is 
more probable, are of organic origin ;—the riband-jasper or striped 
jasper, the finest varieties of which are found in Siberia;—the va¬ 
riously-tinted common jasper ;—the agate jasper, found only in agate 
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 colour, from deep orange yellow to nearly untinged, 
from 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 ;- r 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 ocuius 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-Montan% 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 the silicates of magnesia. 
To the former belongs the table spar or wollastonite from Mount Ve¬ 
suvius, Nagyag, &c. ; perhaps also the alumocalcite of Breithaupt, be¬ 
fore considered as decomposed opal, from Eibenstock, Saxony. 
The silicates of magnesia comprehend 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 Baireuth, 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 heffe- 
hiUite by Dr. Fischer, who discovered it in the Crimea ;—litho?narge, 
the more remarkable varieties of which are, that of a reddish yellow 
