17 
high mountain ranges of Switzerland and Madagascar, are 
never quite pure and transparent. 
The pyramidal or terminal planes are usually smooth 
and strongly lustrous, like glass ; the lateral planes are 
more or less uneven, and striated transversely. The frac¬ 
ture is uneven, splintery, of a resinous lustre, hut never 
vitreous. 
The hardness is = 7, that is, it is harder than felspar, 
and softer than topaz. All the varieties of quartz give 
out bright sparks when struck against steel ; in this process 
small fragments of steel are separated, burn, and melt into 
small nodules. It is not marked by a steel file; glass, 
however, scratches it easily. On a flat steel file it gives 
a shrill sharp sound. The specific gravity is = 2'65, the 
medium weight of all non-metallic minerals and stones, 
with the exception of the precious stones. 
It is insoluble in water and acids ; it is, however, 
attacked and dimmed by fluoric acid. With soda it can 
he melted, while by itself it is quite infusible even in the 
smallest splinters. 
The chemical constituents of pure rock-crystal are pure 
silicates or silicas, oxide of silicon with three equivalents of 
oxygen = Si 0 3 or Si. The bluish-reddish colour of the 
amethyst proceeds from oxide of manganese, the yellow of 
ferruginous quartz from the oxyhydrate of iron, the red 
from oxide of iron, the black smoky topaz from pitch or 
other carbonaceous elements; in short, all these colours 
are extra-essential or accidental. 
The crystallised varieties of quartz occur principally 
in the primary mountains, and in the older stratified rocks, 
amethyst and agate in volcanic minerals and porphyry. 
The finest crystals are found in the Central Alps of Swit¬ 
zerland and in the south-east of France; beautiful single 
crystals, with both sides crystallised, occur in the Marmo- 
rosch and at Bergamo; the former have been called Mar- 
morosch diamonds, because of their lustre. Fine specimens 
of rock-crystal are obtained in many parts of Cumberland, 
Cornwall, Devonshire, Gloucestershire [Bristol diamonds ), 
and other localities in England and Ireland. In Scotland 
they occur particularly fine in the Grampians, and are well 
known as Cairngorms. These have a white, vinous- 
yellow, or fine brown colour, and are much valued as 
stones for ornament. Good crystals are also found on the 
Holy Loch, Argyleshire, at Leadhills, and in the Mull of 
Cantyre. 
The compact quartz is found in layers in gneiss, mica 
schist, and granite ; finely granular compact quartz is called 
quartz-rock, and it occurs in the older stratified rocks as well 
as in the primary formations. It is black and lamelliform, 
or in coarse slates ; it is then called siliceous schist, and 
is used as a touchstone for testing the fineness of gold and 
silver. Quartz in granules is found imbedded in granite, 
gneiss, and micaceous schist, in the itacolumite of Brazil, 
and in many porphyries, as sand quartz occurs abun¬ 
dantly in the upper layers of the earth, in the tertiary, 
diluvial and alluvial rocks, and forms a great part of the 
sandy plains and wastes of Europe, Asia, Africa, America, 
and Australia. In many parts of the earth it contains gold, 
platinum, diamonds, and other precious stones. Sand forms 
an important element of the earth and soil, and bestows 
on it lightness, and affords the conditions which enable the 
roots of plants to imbibe it easily; it is especially useful 
to pines, and the esculent, tuberous, and bulbous roots. 
Quartz sand and pounded quartz are used in the manufac¬ 
ture of glass, porcelain, bricks, mortar, etc.; for white 
glass for mirrors, for optical instruments and porcelain, it 
must be perfectly pure and white. It is an important 
element of the sandstones which are found in most strati¬ 
fied formations, and frequently form extended mountain- 
ranges. Th e fulgorites, or vitrified tubes (Plate IY. Fig. 6), 
are formed by strokes of lightning in the sand, and are 
composed of melted grains of sand ; they are frequently 
from four to six feet long, and divided into several branches 
They are found by shepherds in Northern Germany, in 
the Senner and Liineburg heaths, and are generally some¬ 
what blackened by humus or mould ; externally they are 
rough, and internally vitreous and hollow. The flints 
are found in varying quantities in the white chalk, and 
in single layers of the Jura chalk, in roundish globules, 
sometimes in a tubular form, and sometimes as petrifac¬ 
tions of sea-urchins, mussels, snails, corals, etc. They 
were formerly used, when split into small square pieces, 
for striking lights in the hand, and also for the locks of 
fire-arms. 
Compact quartz rock, granite rich in quartz, gneiss, 
and sandstone, are used in the formation of roads and 
pavements, for millstones, etc. 
Perfectly clear rock-crystal, transparent smoky topaz, 
and unblemished amethyst, are used as ornamental stones 
cut into tabular and rosette shapes; the finest amethysts 
come from Brazil, Ceylon, and Siberia; very fine druces of 
amethysts are found at Schemnitz in Hungary, and in the 
globular jasper of Oberstein, sometimes also at Oppenau 
and Baden. 
Chalcedony, agates of all kinds, carnelians, chrysoprase, 
and even many kinds of jasper, are used also as ornamental 
stones, and for all kinds of objects of art, as boxes, buttons, 
cups, lustres, etc. Chalcedonies of two colours, and onyx, 
are principally used for cameos, and gems, or cut-stones 
and signet-rings; the heliotropes and carnelians are used 
for rings also. This is, indeed, a time-honoured use, which 
was put in practice by the Egyptians, Greeks, and Romans, 
who, as the antique cameos bear witness, even in their time 
knew perfectly well the art of cutting these hard stones. 
The finest chalcedonies come from India, Brazil, and 
the east, where they are found at Brussa, at the foot of 
Olympus; they occur, moreover, in Hungary, Silesia, 
Saxony, France, and in many other countries. At Black- 
down, in England, very fine chalcedonies are found, as 
petrified snails and mussels. 
The blood-red carnelian comes principally from Egypt, 
where it is found in the course of the Nile as far up as 
Nubia, in round nodules (Plate IY. Fig. 2), of all shades. 
The sardonyx , composed of rose-red and white, owes its 
agreeable colour to a layer, in which numerous red spots 
of oxide of iron are interspersed (Plate IY. Fig. 13) ; it 
must formerly have been particularly valued as a ring- 
stone, since the ring of Polycrates was made of it; it has 
also been found at Babylon. The Arabian onyx consists 
of black and white bands (Plate IY. Fig. 10), and was 
also very highly esteemed by the ancients. 
Jasper is found for the most part in large masses in 
the igneous and stratified rocks; very fine brown nodular 
jasper, which receives a remarkably fine polish, showing 
most beautiful annular markings, is found in the course of 
the Nile (Plate III. Fig. 9). Red and yellow jasper (Fig. 
