518 A POPULAR EXPOSITION Of THK 
called asteria sapphires, §c., according to their colour. Red (and 
blue) corundum oecurs sparingly in the crystalline limestone 
(Laurentian series) of Burgess township, Lanark Co., C. W. 
Spinel.—Red, blue, dull-green, black, &c. In small granular 
masses, but chiefly in regular octahedrons, 
simple or modified ; figs. 29, 30. The latter 
figure represents a common twin-form, or 
combination of two octahedrons. fnfusible, 
H. 8°0; sp. gr. 3°5-4°5. Spinel isan alumi- F%s-29. Fig. 30. 
nate of magnesia, but a portion of the magnesia is usually replaced’ 
by oxide of iron, as in the black varieties called pleonaste, more 
especially ; or by oxide of zinc, as in the Swedish dark green variety 
called Gahnite or automolite. Normally, it consists of alumina 72, 
magnesia 28. The clear red varieties are empioyed in jewellery under 
the name of Spinel or Balas ruby. Well-crystallized black speci- 
mens occur in the Laurentian limestone of Burgess township, 
C. W.; and bluish specimens with clintonite (a chioritie, altered 
mineral,) in D’Aillebout, Joliette Co., C. E. 
Magnetic Iron Ore.—Black with black streak, ané in general, 
a sub-metallic lustre. Massive, cr in octahedrons and rhombic 
dodecahedrons. Strongly magnetic, often with polarity. See A 4, 
above. 
Chromic Iron Ore.~-Black ; chiefly massive, and usually with sub- 
metallic lustre. Streak, dark brown. Imparts a fine green colour 
to borax before the blowpipe. See A 4. above. 
Quartz.—A substance of a vitreous or more or less stony aspect ; 
colourless, or of various colours, as purple, brown, red, green, yellow, 
&e. Occurring in crystals and erystalline 
groups, figs. 31, 32, and also in nodular, 
botryoidal, and amorphous masses. The erystals 
are commonly six-sided prisms, streaked across, 
and terminated by a six-sided pyramid. H. 7:0; 
sp. gr. 2°6-2°7. Infusible; but melting (with 
great effervescence) with carbonate ofsoda, into ig.31. Fig. 32. 
a clear glass. Quartz consists normally of pure silica, the coloured 
varieties owing their tints to minute and accidental admixtures of 
sesqui-oxide of iron, bituminous matter, and other inessential ingre- 
dients. Special names have been applied by lapidaries and others to 
