<h2><SPAN name="COMMON_MINERALS_AND_VALUABLE_ORES" id="COMMON_MINERALS_AND_VALUABLE_ORES"></SPAN>COMMON MINERALS AND VALUABLE ORES.</h2>
<p class="ac">THEO. F. BROOKINS.</p>
<p class="ac">I.—IRON MINERALS.</p>
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<p class="drop-cap">PROBABLY many a bright youth,
accustomed to wander through
the fields in enjoyment of nature,
has been thrilled with
pleasurable anticipations on finding, in
some outcrop of crystalline rock, a
mineral substance that glittered as
gold. That his anticipations were premature
should not deter the ambitious
youth. Men far beyond him in experience
have been deceived by that same
"fool's gold." History records that
shiploads of the valueless yellow iron
pyrites were sent to England by explorers
of America on the supposition
that they were accumulating gold.</p>
<p>Of the various compounds of iron
occurring in nature, but four may be
considered as relatively common—pyrite,
magnetite, hematite, and limonite.
Pyrite consists of iron and sulphur;
magnetite, hematite, and limonite are
oxides of iron. The first-named mineral
differs largely from the others in
external appearance as well as in composition.
The others are, however,
readily differentiated. We will discuss
each of the four minerals in the
order mentioned above.</p>
<p>The sulphide of iron, pyrite, occurs
in many crystalline rocks; but, owing
to the difficulty of separating the iron
and sulphur, is not used as an ore of
iron. The mineral much resembles in
external appearance a yellow ore of
copper, called chalcopyrite, from which
it may be distinguished in that it will
strike fire with steel. A specimen of
pyrites containing large crystals is an
interesting subject of study. These
crystals are cubical in shape, but generally
massed together so that no single
crystal form may be observed as
complete. Peculiar striations on the
cube faces may often be noted. The
striations of no two adjoining faces
are continuous; but rather a striation
of one face bears to that of another in
direction the relation of the stem of a
printed T to the top, or vice versa.
Owing to the affinity of each component
element for oxygen, pyrite often
changes to vitriol, or else forms the
oxide of iron, limonite, described below.</p>
<p>The black oxide of iron, magnetite,
occurs widely distributed. As its name
indicates, it sometimes displays the
properties of a magnet. If a fragment
of unequal dimensions be suspended
freely by a string, the longer
dimension will gradually swing into a
north and south direction. The property
possessed by magnetite of attracting
other bits of iron appears to have
been known to the ancients, and by
them the name lodestone was applied
to the mineral. Since the power to
attract other particles of iron is not
apparent in all specimens of magnetite
we must consider other more distinguishing
characteristics. The ore is
very heavy; particles of it are attracted
by an artificial magnet, in which regard
it differs from the other minerals
we have mentioned; if a piece of the
ore be scratched across the surface of
a harder substance, <i>e. g.</i>, smoky quartz,
a black "streak" will be left. Pure
magnetic iron ore is intensely black,
with no coloring.</p>
<p>In a series of ore beds formerly
operated by a mining company of
northern New York, four distinctions
<span class="pagenum"><SPAN name="Page_192" id="Page_192">[Pg 192]</SPAN></span>
of the crude ore were made, two varieties
of blue, one of black, and one of
gray. The blue coloring is apparently
due to the presence of impurities; the
black ore is evidently magnetite; and
the steel-gray mineral, failing in the
characteristic properties of magnetite,
finds its class place under hematite.
Hematite differs from magnetite in
representing a higher degree of oxidation.
It is often found, as indicated
above, in beds distributed in close
conjunction with those of magnetite.
This ore is a valuable source of iron.
Hematite commonly occurs in earthy
materials, as red ochre. Its streak is
red. All rocks of a reddish or red
color owe the color to this oxide of
iron.</p>
<p>When hematite rusts, the brownish-yellow
or yellow iron oxide, limonite,
results. The streak of limonite is yellow,
thus distinguishing it from hematite.
Disseminated through beds of
clay, limonite gives them the characteristic
yellow color. Such clays turn
red when heated, since the water of
the limonite is driven off, leaving
hematite as a residue. This is the explanation
of the usual coloring of
bricks. Yellow ochre is impure, or
earthy, limonite.</p>
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