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The Pamphlet Collection of Sir Robert Stout: Volume 66

Mining and Geology : Economic Minerals. — Coal

page 36

Mining and Geology : Economic Minerals.

Coal.

Coal mines are being worked in the Provincial Districts of Auckland, Nelson, Canterbury, and Otago (including Southland).

The different varieties of coal may be classed as follow:—
Class I.Hydrous, containing an excess of combined water.
  • Lignite.
  • Brown coal.
  • Pitch coal.
Class II.Anhydrous, containing very little combined water.
  • Glance coal.
  • Semi-bituminous coal.
  • Bituminous coal.

I. Hydrous Coal, containing 10 to 20 per cent, of permanent Water.

Lignite shows distinctly woody structure; laminated; very absorbent of water.

Brown Coal rarely shows vegetable structure; fracture irregular, conchoidal; colour dark-brown lustre feeble; cracks readily on exposure to the atmosphere, losing 5 to 10 per cent, of water, which is not reabsorbed; burns slowly; contains resin in large masses.

Pitch Coal.—Structure compact; fracture smooth, conchoidal; jointed in large angular pieces; colour brown or black, lustre waxy; does not desiccate on exposure, nor is it absorbent of water; burns freely; and contains resin disseminated throughout its mass.

II. Anhydrous Coal, containing less than 6 per cent, of Water.

Glance Coal.—Non-caking, massive, compact or friable; fracture cuboidal, splintery; lustre metallic; structure laminated; colour black; does not form a caking coal, but slightly adheres. This variety is brown coal altered by igneous rocks, and presents every intermediate stage from brown coal to anthracite.

Semi-bituminous Coal.—Compact, with laminae of bright and dull coal alternately; fracture irregular; lustre moderate; cakes moderately, or is non-caking.

Bituminous Coal.—Much-jointed, homogeneous, tender and friable; lustre pitch-like, glistening, often iridescent; colour black with a purple hue, powder brownish; cakes strongly, the best varieties forming a vitreous coke, with brilliant metallic lustre.