68 natural history. (Minerals.) [north 
following Case relate to calcedonic substances. Among the specimens 
of common calcedony the most remarkable are, the smalt-blue variety 
from Felsobanya in Transylvania, crystallized in obtuse rhombohedrons; 
the branched and stalactical calcedony from Iceland; the splendid speci¬ 
mens from Cornwall, especially from Trevascus mine, &c.; the botryoi- 
dal, from Feroe; the large hollow geodes from Oberstein; nodules^ 
enclosing water (enhydrites), from Monte Berico, near Vicenza, where 
they occur in volcanic rocks, &c. 
Case 23. Calcedonic substances continued: cut and polished pieces 
of calcedony with red and black dendritic and other figures, called 
mocha-stones; varieties with white, brown, and black, straight or 
curved lines, some of which w T ere probably among the substances of 
which the costly vasa murrhina of the ancients were made; red and 
yellowish varieties of calcedony 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 wdiich calcedony, carnelian, amethyst, and heliotrope generally form 
the predominant ingredients, combined in straight, or more or less 
curved and concentric or zigzag delicate lines, imitating coloured de¬ 
signs of fortifications, &c.: among these may be particularized the beau¬ 
tiful agate-nodule from the trap formation of Central Asia, presented 
by C. Fraser, Esq. 
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, w T hich do not owe their form to rolling, but are probably of 
organic origin: when cut and polished they exhibit various fanciful 
delineations (one of the specimens in the table represents on its 
fractural surface the likeness of Chaucer the poet);—the riband-jasper 
or striped jasper, the finest varieties of which are found in Siberia;—the 
variously-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 jire-opal, ex¬ 
hibiting a suite of colour, 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 
wdien 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 w 7 hen 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 
