Montana oil and mining journal. [volume] (Great Falls, Mont.) 1931-1953, 1941-04-05

rare groups of elements tnat com
Drise collectively about 0.5 percent
of the earth's crust. 1t is metdl
belonging to the oxygen group OF
the peroidic system, which includes
tungsten, molybdenum, and uran-
INN The metal is blue-white with
a permanent brilliant luster when
polished 1t has a hardness of nine,
which is about the hardness of the
sapphire. 1t has a scratch hardness
of 1000 in comparison to l,95O Tor
case-hardened steel, $50 for ordi-
nary shaft steel and 408 for swed-
ish steel. The specific gravity at
so degrees c is 6.92. The atomic
weight is so. 1t melts at 1920 de-
grees c. and bois at 1000 degrees
c.
Since chromium has never been
found in the pure or native state
in nature, 1t is not recognizable
to the ordinary layman or the in
experienced prospector. There are
several ores of chromium, but the
only one of such quantities as TO
be of commercial value is chrO-
mite.
Composition
Chromite Ger. 2O3. FeO) is com
posed in theory by $50 chromium
sesquioxide (Cr203) and 32% of
ferrous oxide (FeO). In deposits it
is never found in these percentages.
Requirements of the iron and chrO-
MUM by magnesium, alumina or
ferric iron alter the percentages in
1t is a compact ore of granular
crystalline structure black to brown
ish in color and sometimes an or
ange brown or yellow color when
extremely weathered. The streak is
brown, it is translucent to Opaque
and has a sub-metallic luster. The
hardness of the ore is SIS, and
its specific gravity is an average
of 4.5. 1t is brittle with an unev-
en- fracture. Where crystals are
fractured the fracture is in appear
ance like specular hematite or
sometimes like the faces of bio
tite mica. This condition is notice
able when the crystals are of I'M
usual size. Ordinarily they are of
a size comparable to sand.
Found In Scrpentine
Chromite is usually found in bas-
ic igncOus or altered basic rocks,
such as serpentine or tale. The
observation-disclosures belt in Mon
tana is confined to the proxene
dixie from one-half mile to one
and one-half miles in width and
about q miles long The gangue
rock here is serpentine. The the
DRY of the origin of chromite is
disputed by some authorities 1t was
generally understood until recent |
ly that the ore was a product OF |
magmatic segregation, but it is dis |
regarded as correct by some who |
have found evidence that the ores |
We're introduced after the solidi-
fication of the bearing rock |
magma.
The ore bodies occur in dissent
mated and compact masses, lenses,
stringers and veins. Until the dis
coYery of the veins no one dis
credited the theory of magmatic Sc
gregation.
Iron Content Undesirable
The consumption of chromium
has, in the past, been governed by
the ratio of iron to the amount of
chromium present In the mined
ores. High iron ratios are unde-
sirable in the present reducing pro-
cesses because it makes a more
iuseable product in refractory ores
ana also lessons the value and the
percentage of chromium in ferro-
chromium. The industries ND until
lHls time have tried to maintain as
nearly as possible a ratio of one
part IRON to three parts chromium
However the consumption average
mas been near to 1:21b Foreign
ores nave chromium oxide content
OF from As to 55 percent. The do
hestic ores of the United States are
III the neighborhood OF 40 percent
win nigh relative iron content
Gravity concentration can raise
the chrome content but il con
sequently raises the iron in the
same ratio. But by concentrating
ores 1t is possible to some extent
10 separate the Objectionable siIi-
ca alumina and magnesia which
increases the loss in reduction
- - - RUoSiUle LOT the n |
dustry to obtain lump ore rather
than concentrates, they are inclin-
ed to do so, since there is room for
an additional loss up to ten percent
in fine materials
Uses OF Chromium
The uses of chromium are di-
vided into three major divisions
of industry; Metallurgical $3.50
(40%), and chemical
(15%).
Metallurgical uses are of two
types, that of metallic chromium and
that of ferrochromium. Metallic
chromium is used mostly in the
making of nOn-ferrous alloys, high
content chrome steel and chrome
plating. Several methods of the
reduction of metallic chromium are
used commercially. A few are: ell.
ectrolysis of chromium compound
reduction of Cr203 by
Jhe thermic process, and reduction
Of Cr2O3 with carbon in an cleo
.ric furnace.
/