14 
twin crystals are also found (Fig. 23) in aggregations of two 
half octahedrons. It is found white, red, blue, green, and 
black, highly lustrous, capable of polish, transparent, opaque, 
of 8° of hardness, and of a specific gravity from 3‘5—3*8. 
The constituent elements vary according to the colour 
and occurrence; there are magnesia, lime, iron, and zinc 
spinels; many of the Ceylon varieties contain some oxide 
of chrome, others silica. The usual formula = RR, R 
representing magnesia, lime, oxide of zinc, and protoxide of 
iron, and R alumina, and sometimes oxide of iron and chro¬ 
mium. Ulrich found in the red varieties of Ceylon, 26‘21 
magnesia, 071 protoxide of iron, 600 alumina, 1*10 oxide 
of chrome, and 2‘02 silica. Insoluble in acids, infusible 
before the blowpipe, fusible with borax to a glass, from 
which salt of phosphorus generally separates some silica. 
The red varieties, on being heated, become brown and 
black; on cooling, however, they first assume a green, 
then a white, and at last again assume their original red 
colour. The black pleonaste gives a strong reaction of iron, 
the galmite or automolite, with borax, gives a schlag of zinc. 
The deep-red spinel is called spinel ruby , the rose-red 
balais, the black pleonaste or ceyIonite, the green chlorospi- 
nel, and that which contains zinc automolite or galmite. 
The two first rank as precious stones; they are, however, 
of less value than the oriental ruby, and are also inferior 
in hardness. They are found sometimes in the mud thrown 
up by rivers, as, for instance, in Ceylon; sometimes in 
volcanic remains, as at Auvergne, on the Rhine, in the 
Fassathal, at Vesuvius, rarely in granite and primary chalk, 
as at Aker in Sweden. 
Figs. 24-27.— Zircon or Hyacinth. 
Quadratic octahedron and prism, the octahedral planes 
placed either on the lateral planes (Fig. 24), or on the 
lateral edges (Fig. 25), or on the truncations of these 
(Fig. 26). 
Colour; yellowish, reddish, brown, green, transparent 
to opaque. The transparent varieties are all valuable, and 
are used as ornaments under the name of oriental hya¬ 
cinths, as seen in Fig. 27 ; they receive a magnificent 
polish. Hardness — 7*5, specific gravity = 44—4 - 5. 
Composition 1 of zircon to 1 of silicic acid = Zr Si, with 
traces of oxide of iron and lime. 
Insoluble in acids, infusible, fusible along with borax 
to a greenish glass, from which salt, of phosphorus sepa¬ 
rates silica in abundance. Is found in the granite of 
Miask, in the syenite of South Norway, in the volcanic 
minerals of Auvergne, and in the mud banks of Ceylon; 
here especially the yellow-brown hyacinth is found, which 
is worth from £4 to £6 a carat. 
Figs. 28-33.— Beryl and Emerald, 
Hexagonal prism (Fig. 28), with truncation of the 
basal edges (Fig. 29), or of the lateral edges (Fig. 30), or 
of both (Fig. 31)._ The yellowish-green (Figs. 28, 29), is 
called beryl , the bluish-green aquamarine (Figs. 30 and 33), 
the deep-green (Figs. 31, 32), emerald. Only the trans¬ 
parent varieties are considered as precious stones; the 
deep-green emerald is the most valuable, one carat being 
valued at from £2 :10s. to £5; beryls, on the other hand, 
are cheaper than the topaz. 
Hardness, 7*5—8'0 ; specific gravity, 2'68—2*73. Fu¬ 
sible in splinters; insoluble in acids. Composition, sili¬ 
cate of berylla (glucina), with silicate of alumina (Be Si 2 
+ Al Si 2 ) ; the colour is derived from a little oxide of iron 
and chromium, which are seen when melted with borax. 
The emerald has smooth lateral planes; those of the 
beryl are situated in a longitudinal direction; on the other 
hand, the terminal planes of the emerald are dim or rough, 
while those of the beryl are mostly smooth. It is the 
lightest of all gems, properly so called. 
The emerald is found in Egypt, where they were 
known to the ancients; in Peru, and in the limestone of 
Muzo in New Granada, of surpassing beauty and size ; in 
the mica-slate of the Urals very large, but seldom quite 
pure, and at Salzburg; the beryl is found in Siberia, North 
America, in Silesia, and in the Bavarian forest near Zwie- 
fel, at Limoges and Alenqon in France. 
PLATE II. 
Figs. 1-7.— Topaz. 
The topaz has for its primary form a right rhombic 
prism (Fig. 1) ; it is generally columnar, and striated ver¬ 
tically, and may be split in the direction of the even terminal 
planes. It has the eighth degree of hardness, and a specific 
gravity from 349—3 - 56. Like the diamond, it is highly lus¬ 
trous, and receives a magnificent polish. The colour is 
white, vinous yellow (Fig. 2), brownish-yellow (Fig. 3), or 
sea-green (Fig. 4); the transparent varieties are known 
as aquamarine. The dark-yellow varieties, on being 
cautiously heated, become rose-red, and are then called 
balais rubies , a name which is also applied to the rose- 
red spinel. 
The dark yellow (Fig. 6) are the most highly esteemed ; 
they resemble the hyacinths so much as to be sometimes 
sold for them. 
It is insoluble in acids, infusible before the blowpipe ; 
with borax it forms a transparent glass, from which the 
silica may be separated by salt of phosphorus. The ele¬ 
ments are—silicate of alumina, with fluoride of alumina (3 
Al FI 3 + 2 Si FI 3 + 6 Ai 3 Si 2 ). 
It is found in the primary rocks of the Schnecken- 
stein, near Auerbach, in Voigtland (Fig. 2), in Saxony and 
Bohemia, where it is mostly white, at Ekatherinenburg 
(Fig. 4), and also in the mud-banks of Brazil, in India, Asia 
Minor, etc. The transparent varieties are called noble, the 
opaque, common topazes; the latter, if they are widely 
separated from one another, as for instance at Altenberg 
and Schlakenwald, in the Erzgebirge, receive the name of 
pycnite , if they occur in a mass, as at Finbo and Braddo 
in Sweden, pyrophysalite. It is fusible in fine splinters. 
Only the pure white stones, especially those from Brazil, 
and the yellow and green ones, which are perfectly trans¬ 
parent and free from blemishes, are considered as precious 
stones. 
