27 
4 
as Fig. 8, the ichthyophthalmite proper, which is distin¬ 
guished from the other zeolites by the silicate of lime 
taking the place of the silicate of alumina. It is in fact a 
combination of double silicate of potash, with eight equi¬ 
valents of simple silicate of lime, and sixteen equivalents 
of water, according to the formula : K, Si 2 + 8 Ca Si + 
16 H. It has a hardness of 4-5 to 5*0, a specific gravity 
0 f 2-3—2*46, and is decomposed by acids; it melts 
readily before the blowpipe, swells up, colours the flame a 
yellow-red, and gives off water in the matrass. The colour 
varies from a glassy transparency to rose-red and brown. 
Apophyllite is found especially at Andreasberg, in the 
Hartz mountains, and in the Faroe Islands; colourless 
crystals occur in Iceland and at Yicenza; the reddish and 
yellow ichthyophthalmites in the Fassathal, at the Seisser 
Alps; the milk-white albine at Aussig, in Bohemia. 
The pectolite , radiated-fibrous, globulous, of pearly to 
silky lustre, of 5*0 hardness, and 2*69 specific gravity, be¬ 
longs also to this species. It contains, however, with the 
silicate of lime, silicate of soda, and a little water, accord¬ 
ing to the formula : 3 Na Si + 4 Ca 3 Si 2 + 3 H. It is 
white, passing into yellowish and grey, and is found in 
the amygdaloids of Monte Balco, and in the Fassathal. 
The wollastonite or table-spar , oblique rhombic, white 
passing into grey and reddish, of vitreous lustre, 4*5—5*0 
hardness, and 2*8 specific gravity, is a pure silicate of lime, 
containing 51*60 of silicate acid, and 46*41 of lime, accord¬ 
ing to the formula: Ca 3 Si 2 . It melts without intumes¬ 
cence, burns brightly, and colours the flame a yellow-red. 
Is found at Auerbach on the Bergstrass, in radiated foliated 
masses; in Hungary, Finland, Pennsylvania, etc. 
The okenite is nearly related to the apophyllite, occurs 
in fibrous radiated masses, and consists of silicate of lime 
and water, according to the formulaCa 3 Si 4 + 6 H. It 
is colourless, passing into yellow and bluish, of pearly 
lustre, translucent, of 4*5—5*0 hardness, and 2*28 specific 
gravity, is decomposed by hydrochloric acid, and comports 
itself otherwise like apophyllite. It is found in the amyg¬ 
daloid of the Faroes, and of Iceland. 
The datholite crystallises in oblique rhombic prisms, 
with different truncations of edges and angles, sometimes 
in clusters and fibrous botryolite and fibrous datholite. It 
is colourless, passing into grey, yellow, and green, friable, 
of vitreous lustre, translucent, cleavage in the direction of 
the lateral planes ; the hardness — 5—5*5, the specific gra¬ 
vity = 2*95—3*0. Melts with intumescence to a trans¬ 
parent glass; when melted with salt of phosphorus it 
gives the yellow-green flame of boracic acid, and consists 
of borate and silicate of lime with water, according to the 
formula: Ca 3 Si 4 + 3 Ca B + 3 H. Occurs by prefer¬ 
ence at Andreasberg, the Hartz mountains, and at Kongs- 
berg in Norway; also in Connecticut, New Jersey, and 
at Sonthose in Bavaria, and at Klause in the Tyrol; 
the botryolite at Arendal in Norway. 
VI. CALCAREOUS MINERALS. 
PLATE VII., Figs. 9-18, and PLATES 
Carbonate of Lime. > 
Lime is one of the most widely distributed metallic 
oxides, and it performs an important part not only in the 
mineral, but also in the vegetable and animal worlds, since 
it constitutes an essential element of fixed organic frames. 
Phosphate and carbonate of lime, and sometimes also sul¬ 
phate, oxalate, and malate of lime occur in most plants, the 
two first especially, in the ashes, and these two are again 
found in the bones and teeth of the higher animals, in the 
shells and coverings of the molluscs and crustaceans, in the 
dermal skeletons of the radiata, and in the stony habitations 
of the polypes. The carbonate of lime is most widely dis¬ 
tributed in the mineral kingdom, the sulphate more spa¬ 
ringly, and more so still, the phosphate of lime ; fluoride of 
lime is found chiefly in the metallic veins. 
All these combinations of lime are, in their pure con¬ 
dition, colourless, and have a moderate hardness and 
weight; calcium itself has a specific gravity of only 1*577. 
They burn before the blowpipe with a white light, some¬ 
times so brilliantly, that they blind the eyes (this is most 
strongly manifested with carbonate of lime), and colour the 
flame a yellowish red, especially when the specimen to be 
tested has been dipped in tallow or wetted with hydrochloric 
acid. The carbonate of lime occurs in two principal forms, 
which, although of the same chemical constitution, yet pos- 
VIII., IX., X. and XI., Figs. 1 and 2. 
sess many physical distinctions, and so form one of the 
finest samples of dimorphism. The crystallisation is rhom- 
bohedral and right rhombic or prismatic ; both varieties are 
composed of simple carbonate of lime, and the former has 
been called calcite , the latter arragonite. Both dissolve with 
effervescence in acids, and when burned give off 1 equiva¬ 
lent of carbonic acid = 43*972, leaving 56*028 of caustic 
lime; the calcite, however, preserves its form during the 
burning, while arragonite falls to a heap of pulverulent 
atoms. Arragonite is also always harder and heavier than 
calc-spar. Both occur crystallised, crystalline, fibrous, and 
compact; the latter varieties are commonly called lime¬ 
stone ; the arragonites can, however, always be distinguish¬ 
ed by its greater hardness and weight, which varies from 
2*8—3*0, and they cannot be scratched by calc-spar crys¬ 
tals ; while, on the contrary, the rhomboidal limestones can 
be scratched by the crystals of arragonite. In their rela¬ 
tions to light they also differ essentially; both, indeed, re¬ 
fract light doubly, but calcite has only one, while arrago¬ 
nite possesses two optical axes-—the fracture also differs 
much, the calcite, however it is crystallised, may be split 
into rhombohedral tables in three directions, while arragonite 
may generally be split, with difficulty however, in the di¬ 
rection of the rhombic prism and the planes of truncation 
of the acute lateral edges, and always presents uneven 
planes of fracture in the direction of the basal planes. 
