16 
Figs. 31-34. —Turquoise, Calaite. 
The turquoise is neither transparent nor very hard, 
and therefore without a trace of crystalline form or struc¬ 
ture, yet it was formerly used as an ornamental stone, for 
which its beautiful colour renders it suitable. 
It is found in irregular crust-like masses (Fig. 31), or 
as a shell over aluminous minerals (Fig. 32), and is pre¬ 
pared for cutting by sawing into peculiar roundish or 
square pieces. The fracture is even and dull, the colour 
verdigris to apple green (Fig. 32, 33), or bluish green 
(Fig. 34), the lustre is slight after polishing, porcellanous ; 
the hardness = 6 ; the specific gravity = 2'86—3'0 ; the 
streak is white. 
It is soluble in acids, infusible before the blowpipe, 
and with borax gives a feeble copper and iron reaction. 
The constituent elements are phosphate of alumina, 
with water, which amounts to about 10 per cent. For¬ 
mula Al 4 P 3 + 9 H + 2 A1 II s . 
The fine turquoises used as ornaments (Fig. 32-34) 
are found in the ferriferous siliceous schists at New 
Madan in Persia, the calaite or johnite (fig. 31) near Jor- 
dansmuhle in Silesia, also at Reichenbach and Planen in 
Yoigtland. 
Figs. 35, 36.— Lazurite or Lapis Lazuli. 
This mineral crystallises in rhombic dodecahedrons 
(see Fig. 8 of this plate) ; it mostly occurs, however, in 
crystalline granular masses of varying capability of cleav¬ 
age, of uneven fracture, and feeble vitreous lustre, but 
slightly translucent, sky-blue to a deep azure; the streak 
light blue. Hardness = 5 - 5 ; specific gravity, 2*5—2*9. 
Chemical constitution—a combination of silicic acid, 
with alumina, lime, magnesia, and soda, and some sulphate 
of sodium or sulphate of iron. 
The colour is destroyed by hydrochloric acid. White 
sulphuretted hydrogen is given off, and silicic acid is 
separated in the form of jelly. 
Before the blowpipe flame it is tolerably easily fusible 
to a white glass, easily soluble in borax, leaving a little 
water on the charcoal. 
It is found in gangues of granite and in granular 
chalk in Siberia, Thibet, China, and Bucharia, and was 
known to the ancients under the name of sapphire. When 
cut it is used as an ornament for mosaics and architectural 
decorations, boxes, vases, etc. Formerly it was principally 
used in the preparation of the valuable artists’ colour, ultra- 
marine, which is now, however, largely prepared by an 
artificial process. 
PLATES III. AND IV. 
Quartz, Silica, and Silicates. 
These very frequent and widely-distributed minerals 
present an extraordinary diversity in form, colour, occur¬ 
rence, and applicability. The crystallised varieties, if they 
are colourless, are called rock crystals (Figs. 4, 6, 7) ; if 
rose-red, rose-quartz (Fig. 3) ; if black or brown, smoky 
topaz (Fig. 4) ; if yellow, citrine / if violet, amethyst (Figs. 
5, 8) ; if milky, cloudy milky quartz ; if they are coloured 
red or yellow by oxide of iron, and non-transparent (Fig. 
1), they are named ferruginous quartz; if they contain 
small acicular crystals of other coloured minerals, needle 
quartz y if they are opaque and colourless, common quartz. 
The compact, non-transparent, and finely-coloured 
varieties, which are capable of taking on a polish, are 
called jaspers , globulous jasper (Figs. 9 and 10), if in 
rounded masses, and riband jasper if they are flat and 
striped. The dark green jaspers, studded with red spots, 
are called heliotropes. The translucent, fibrous, crystalline 
varieties, are called chalcedony , if they are of a single 
colour ; the blood-red are carnelians (Fig. 14, and Plate 
IV., Fig. 2) ; those which are colourless, with arborescent 
figures in their interior, are named moss agate or Mocha 
stone (Fig. 15) ; the yellow are riband agate or yelloio 
chalcedony. The single-coloured, compact, translucent, 
dark yellow, or grey quartz (Plate IV., Fig. 1), is called 
flint; if it presents a distinct grain, however, it is known 
as horn-stone. Many-coloured chalcedonies are generally 
called agates, and according to their different markings— 
fortification agate (Plate IV., Fig. 3), cloudy agate (Fig. 4), 
ribbon agate (Figs. 9, 10, 11, and 12) ; when different 
colours lie above one another, the stone is called onyx 
(Fig. 14), and if it is red and white, a sard or sardonyx 
(Fig. 13) ; spotted agate (Fig. 15), with red or brown spots 
appearing ; ruin or brecciated agate (Fig. 16), if they appear 
to be composed of fragments, variegated striped agate (Fig. 
17 and 18), if they are striped with different colours. The 
single-coloured apple-green chalcedonies (Fig. 8) are called 
chrysoprase ; mottled quartz, composed of round masses, 
is called pudding-stone or conglomerate (Fig. 5). 
Quartz, like the corundite and calcareous spar, has 
for its primary form the rhombic hexagon, which, how¬ 
ever, does not occur by itself; on the contrary, the most 
usual form of the crystals is a hexagonal prism, combined 
with the hexagonal double pyramid (Plate III., Figs. 3 
and 6), more rarely the pyramid (Fig. 1) occurs alone, 
more rarely still the rhombohedron occurs with the hexa¬ 
gonal prism or simple truncation of the six basal angles 
(Fig. 2). 
The most interesting peculiarity of the rock crystals 
is, however, the great variety which arises from the diffe¬ 
rent extensions of single planes or pairs of planes, for they 
are seldom so regular as those in Figs. 1-3. Already in 
Figs. 4 and 5 the pyramidal planes alone are present; in 
Fig. 6 these planes are very unequal, stretching down¬ 
wards to a greater or less distance ; in the group of 
crystals (Fig. 7) from Dauphine, one terminal plane is 
principally extended at the expense of the others, and two 
of the six lateral planes are usually greater than the other 
four. Besides, simple or double, and one-sided truncation 
occurs at every three basal angles, the last is either on the 
right or left; further, there is simple and double truncation 
of the six basal edges, or of three of them only (Plate B, 
Fig. 6), which distinguishes a combination with other six, 
or three-sided pyramids. 
The crystals sometimes reach the extraordinary size of 
two feet in breadth, by from three to six in length ; but 
those large specimens which are found principally in the 
