MINERALS AND GEOLOGY OF CANADA. 9 
combinations. ‘The principal minerals comprise: Augite, Horn- 
blende, Epidote, Orthoclase, or potash feldspar, Stilbite, and Gypsum, 
Fie. 19. Fra. 20. 
The Triclinic, or Doubly Oblique system.—The forms of ° this 
system are oblique (or they incline) in two directions. The crystals in 
® ceneral are more or less flat and unsymmetrical in appearance. No 
two planes meet at right angles; and there are never more than two 
similar planes present in any crystal belonging to the group. Axi- 
nite, Albite or soda feldspar, Labradorite or lime feldspar, and 
sulphate of copper, are the principal triclinic minerals. 
Such is a brief exposition of the six crystal systems. For present 
purposes it will only be necessary for the student to impress upon 
his memory the following forms, so as to be able to recognize them 
when met with. The cube (Fig. 1), the regular octahedron (8), the 
rhombic dodecahedron (2), the pentagonal dodecahedron (5), the 
cubo-octahedron (6), the regular six-sided prism (10), a combination 
of a six-sided prism and pyramid (12) a rhombohedron (18 and 14), 
a scalenohedron (15), a rhombic prism (16). 
The irregular forms presented by minerals are of very subordinate 
importance; so that a few of the more common need only be men- 
tioned. Most of the terms used in reference to these, explain 
themselves. 
Irregular mineral forms :—Globular or nodular, ex. quartz, iron 
pyrites ; reniform or kidney-shaped, ex. quartz, &c. ; botryoidal 
mammillated: a form made up of a series of rounded elevations and 
depressions, or otherwise exhibiting a surface of this character, ex. 
red and brown iron ore, calcedony, &c.; stalactitic, ex. cale spar, 
&c.; coralliform, resembling certain branching corals, ex. arragonite ; 
dendritic or arborescent, a branching form, often made up of small 
aggregated crystals, ex. native silver, native copper, &c.; filiform or 
wire-like, ex. native silver: acicular, in needle-like crystallizations, 
ex. many varieties of augite, hornblende, epidote, &c. When a 
