77.—WlLLEMITE.
Occurs
in crystals and masses; feeble lustre; brittle; can hardly be cut with
a knife; sometimes scratches glass; (makes a jelly in muriatic acid ;
gravity 4.
Value.—Contains seventy per cent, of zinc.
Localities.—Found in limestone with zincite.
78.—Zincite.
Occurs in foliated masses or grains, powder orange-yellow ; brittle ; dissolves in acids without effervescence; gravity S-5.
Value.—Yields seventy-five per cent, of zinc.
Localities.—Found in limestone with Ftankliniie Garnet, etc.
prospecting for diamonds, gold, sli.ver, copper, Lead and Iron.
The
mineral riches of a country are frequently discovered by attentively
observing the fragments brought down by the action of water from the
hills into the valleys; and on traciag these to their several sources,
the veins from which they were originally detached, are in many
instances found. Water also acts in another way a very important part
in the discovery of mineral veins, as by closely examining the faces of
the different gullies and ravines, which intersect a country, a ready
means is afforded of ascertaining whether its strata are traversed by
metalliferous deposits; and, therefore, in exploring with a view to its
mineral productions, no opportunity should be lost of observing the
various sections thus naturally laid bare.
When
fragments of an ore are found on a hill-side, it is very evident that
the vein must lie higher up. If the vein is horizontal and the
fragments are found on the top of the hill, there is no probability of
finding much if any of the vein, for generally it has been washed away.
Ore-veins, however, are almost always nearly vertical; so that boring
is of little use, as it might pass by the richest vein, or, striking it
lengthwise, give a too favorable result.
As heavy minerals do not drift far, metals are always found near their source.
Horizontal beds can be worked at the least cost.
Pockets and nodules, or any detached masses of minerals, are soon exhausted. Veins, lodes and beds are most valuable.
Boring
a three-inch hole, which costs about $1 a foot, is a good method of
testing a mineral vein or bed which lies more or less horizontally. A
shaft may be sunk in sandstone for from $6 to $3 per cubic yard; in
slate and gravel, at from |2 to $1.
The existence of mineral springs, and the rapid melting of the snow in any locality, arc no indications of ores.
Searching for Diamonds.—Few
things are so unpromising and unattractive as gems in their native
state. Hence their slow discovery. There is little doubt that diamonds
exist in many places as yet unknown, or where their presence is
unsuspected. It is very difficult for the unpractised eye to
distinguish them from crystals of quartz or topaz. The color
constitutes the main difficulty in detecting their presence. They are
of various shades of yellowish brown, green blue and rose-red, and thus
closely resemble the common gravel by which they are surrounded. Often
they are not unlike a lump of gum arabic, neither brilliant nor
transparent. The finest, however, are colorless, and appear like
rock-crystals.
In
Brazil, where great numbers of diamonds, chiefly of small size, have
been discovered, the method ,of searching for them is'to wash the sand
of certain rivers in a manner precisely similar to that employed in the
gold fields, namely, by prospecting pans. A shovelful of earth is
thrown into the
