INTRODUCTION. 
The Natural History of the Mineral Kingdom comprises, 
in its widest signification, the inorganic fixed bodies which 
form the earth’s crust. Mineralogy, in a narrower sense, 
treats of the simple minerals, Geognosy, of masses of rock 
presented as a whole, while Geology is occupied with the 
theory and history of the formation of the globe. Most 
minerals are fixed or solid, and characterised by pecu¬ 
liarity of form, appearance, weight, hardness, lustre, colour, 
etc. They are inanimate, having their origin in chemical 
activity and the physical forces, and present no traces 
of organic structure. They are under the influence 
of no relations to climate, and although they sometimes 
occur in conditions which admit of their being dissolved in 
the atmosphere, or of their being decomposed, yet, in 
comparison with the organic bodies of the earth, they 
present a certain permanence and durability, so that when 
we wish to produce anything durable either in art or in 
industry, we usually have recourse to the products of the 
mineral kingdom. 
FORM OF MINERALS. 
As regards the relations of form, we find in simple 
minerals either very regular many-sided bodies, which 
are called Crystals, or irregularly shaped forms, which 
are not crystallised. Crystals are bounded by a certain 
number of planes or faces, edges and angles, the form, 
position, and extent of which are subject to the laws of 
symmetry. 
The crystalline planes are in general smooth, as all the 
figures in Plate A show, and only exceptionally striated, 
either in the line of certain edges, as in Plate B, Fig. 2, 
vertically, as in Fig. 5, or horizontally, as in Fig. 6. They 
are also occasionally covered with smaller crystalline planes, 
the arrangement of which is said to be glandular, as in 
Plate B, Fig. 4, scalariform, or ladder-like, as in Plate XI., 
Fig. 21, etc.; more rarely, they are sometimes curved, as 
in Plate B, Fig. 1, and Plate I., Fig. 4. According to 
the number of their sides and angles we distinguish— 
I. The Square, or four-sided figure; and further, 
a. The Square, or equal-sided rectangular parallelo¬ 
gram. Plate A, Fig. 1: 
b. The Rhomb, or equal-sided oblique angled 
parallelogram. Fig. 3. 
c. The Rectangle, or unequal-sided rectangular 
parallelogram. Fig. 5. 
d. The Rhomboid, or unequal-sided oblique angled 
parallelogram. 
e. The Trapezium, or unequal-sided square, with 
two parallel sides. Fig. 9. 
f The Trapezoid, in which every two adjacent 
sides are equal to one another. 
II. The Triangle, or three-sided figure. 
a. The equal-sided, or regular triangle. Fig. 13. 
b. Isoceles triangle, with two sides equal. Fig. 15. 
c. Unequal-sided triangle, with three unequal 
sides. Fig. 17. 
III. The Pentagon, or five-sided figure. Those examples 
which occur in the mineral kingdom are irregular, 
so that one side is generally larger than the other 
four. Fig. 19. 
IV. The Hexagon, or six-sided figure, may be regular, 
as in Fig. 21, having six equal sides cutting each 
other at equal angles ; or irregular, in which case 
the angles are usually of two kinds. 
V. The Octagon, or eight-sided figure. Fig. 23. 
YI. The Dodecagon, or twelve-sided figure, Fig. 25, etc. 
This occurs almost always in composite forms, and 
presents corresponding variations. 
According to the number of planes we recognise— 
I. The Tetrahedron, bounded by four triangular planes. 
Plate XY., Fig. 17. 
II. The Hexahedron, bounded by six square faces. Plate 
A, Figs. 2, 6, 8. 
III. Octahedron, bounded by eight triangular faces. Plate 
A, Figs. 11, 16, 18. 
IY. Dodecahedron, bounded by twelve faces. Plate A, 
Figs. 4, 20. 
Y. Icosahedron, bounded by twenty faces. Plate XVII., 
Fig. 8. 
VI. Trapezohedron, bounded by twenty-four faces, each 
of the form of a trapezium. Plate A, Figs. 10, 
12 . 
VII. Hexakisoctahedron, bounded by forty-eight scalene 
triangles. Plate B, Fig. 1. 
