18 
10), is found in the pea-ironstone at Kandern and Auggen 
in the highlands of Baden, where it frequently contains a 
number of small snails. The ancients manufactured whole 
pillars of jasper for temples, altar-pieces, etc. In Russia, 
the ribbon-jasper (Plate III. Fig. 11), is still cut into all 
kinds of artistic objects. In Florence and Naples, all these 
stones together are employed in the manufacture of tables 
inlaid with the most beautiful flowers, leaf-work, and mosaic 
borders. 
Pudding-stone, a kind of natural mosaic, composed 
of different-coloured nodules of quartz, held together 
by masses of quartz (Plate IV. Fig. 5), is found in 
England and Hungary, and is likewise employed in the arts. 
Ghrysoprase is a finely granular or compact quartz, 
coloured green by oxide of nickel, slightly translucent 
(Plate IV. Fig. 8), which, so far as we are aware, occurs 
only in the serpentine rocks at Kosemitz in Silesia, and 
is likewise used as an ornament. 
PLATE IV. 
Figs. 7, 19, 20.—Opal or Amorphous Quartz. 
These minerals are distinguished by their irregular 
form, which is without any trace of crystalline shape or 
structure; by their flat or conchoidal vitreous fracture, 
small density and friability, and also by their small degree 
of hardness (=5’5 —6), and weight (=2‘0 —2*2), compared 
with crystalline quartz. The chemical constituents are 
silica, with 3— 10 per cent of water. It is also soluble in 
potash ley. 
There are colourless transparent opals which are called 
glass or water opals {hyalite), coloured, variegated, translu¬ 
cent and clouded, dark coloured, and even black opals. 
The most valuable is the noble opal (Fig. 19), which is 
milky white, and exhibits a rich play of all the colours of 
the rainbow. This magnificent play of colours, combined 
with sparkling glimmer and lustre, cannot easily be 
represented in a plate. It is found in a porphyrytic 
mineral at Eperies and Czervenitza in Hungary; it is 
cut for ornament in a roundish form, and is very highly 
valued. 
The fire-opal, almost transparent, and exhibiting a play 
of various colours, with yellowish flashes, occurs at Zima- 
pan, San Miguel, in Mexico, also at the Azores, and at 
the Faroe Islands. Those from the first locality are most 
highly valued, and are also used as stones for ornament. 
The green opal (Fig. 20) is found of remarkable 
beauty at Kosemitz in Silesia, and at Pernstein in Moravia. 
At these other places in Saxony, Bohemia, and Hungary, 
the common and so-called semi-opal are found in all 
colours and forms. 
The wood opal (Fig. 7) is wood petrified by a mass of 
opal. The piece figured is a pine, with distinct concen¬ 
tric rings marking the age of the tree, and of perfectly 
opaline fracture, from Hungary. It is made into 
boxes, etc. 
Besides these, silicic acid forms with the bases (earths 
and metallic oxides), many of the various combinations 
which in general are called silicates, as, for example, most 
precious stones, all felspars, zeolites, micas, clays, the 
minerals formed from or consisting of these ; thus also 
the soils and earths contain much silica, from which it 
passes abundantly into the bodies of plants, and from these 
again into the animal frame. In the stems of the tree¬ 
like grasses (Bambusa) it forms itself into thick opal-like 
bulbs, which are known under the name of tabasheer. 
PLATE V. 
Figs. 1 and 2 .—Cyanite or Disthene. 
Gyanite takes its place among the precious stones from 
its hardness, appearance, and chemical composition; but, 
on account of its wanting the necessary purity, it can 
rarely be cut and used as an ornament. 
The primary form is an oblique rhomboidal prism of 
106° 50' and 73° 45 Q the inclination of the terminal 
planes towards the narrow lateral planes is 100° 50 1 and 
79° 10 r ; the lateral edges are in general truncated, as seen 
in Fig. 4, or there are two crystals aggregated as twins 
(Fig. 2). The fracture is uneven, the crystals may be 
split in the direction of the large lateral planes, and they 
are also curved. 
Hardness = 6—7, specific gravity 3’55—3‘67. 
Generally light sky-blue to white, yellow, brown, or 
black; the latter varieties are called rhcetizite, especially 
if they are radiatingly foliated; the streak is white. 
Infusible and insoluble in acids, reducible to glass, 
however, with borax. 
Elements: silicate of alumina = Al 3 Si, with 68-994 
of clay and 31-006 of silicic acid. 
It is found frequently in the micaceous schists of the 
Gotthardt and the Tyrol, in Scotland, Pennsylvania, also 
in the gneiss and granite, as, for instance, in Pfitsch in 
the Tyrol, and at Breitenbronn in Saxony. 
The fine blue transparent varieties are cut as stones 
for pins and rings. Very pure fragments, especially those 
from the East Indies, have been sold as sapphire; they 
may, however, easily be distinguished from these by their 
inferior degree of hardness. 
Figs. 3-5.— Staurolite. 
Staurolite is a mineral nearly related to the foregoing, 
of a dark or brownish-red colour, which crystallises in 
right rhombic prisms (Fig. 3). Truncations of the acute 
lateral edges (Fig. 4) and of the obtuse basal angles occur, 
and very frequently also twins joined in the form of a cross 
at right (Fig. 5) or oblique angles, or united perpendicu¬ 
larly to one another. 
For the most part it is opaque or translucent, brown¬ 
ish-red, of the colour of common garnet. 
Hardness 7—7‘5 ; specific gravity 37—3-8. 
Chemical elements : silicate of alumina, with aluminate 
of the oxide of iron (3 Al Si + Fe Al 3 ). 
