PHYSICAL PROPERTIES:
Chemistry: PbS
Composition: Lead Sulfide
Class: Sulfides
Group: Galena
Crystal system: isometric
Fracture: uneven
Hardness: 2.5
Specific gravity: 7.5
Luster: metallic
Streak: gray
Cleavage: perfect in four directions
Color: dull to silver gray sometimes with
a bluish tint.
Transparency: crystals are opaque
Associated Minerals: calcite, chalcopyrite,
barite, dolomite, fluorite, quartz, sphalerite, siderite, pyrite and
other sulfide minerals, also lead oxidation minerals such as cerussite
and anglesite.
COMPOSITION:
(86.6% lead, 13.4% sulfur). Often contains silver, arsenic, antimony,
and other impurities. The structure of Galena is identical to
that of halite, NaCl. The two minerals have the same crystal shapes,
symmetry and cleavage. Through alteration, galena produces many other
lead minerals like anglesite, cerussite, and phosgenite.
DISTINGUISHING CHARACTERISTICS:
The cubic cleavage with the lead-gray metallic color and luster is characteristic.
Might be confused with dark sphalerite, in which case the light streak
of the sphalerite would permit a distinction. Other similar sulfides
have good cleavages in a single direction, but not in three. The blowpipe
reactions will help in very fine-grained (and deceptive) varieties.
Sphalerite - lacks cubic cleavage, lighter (3.9 - 4.1),
streak (light brown to nearly white)
Stibnite - lacks fine cleavage, different crystal form Acanthite/Argentite
- softer (2), is sectile Jamesonite - lacks fine cleavage, slightly
lighter in weight (5.5 - 6.0), different crystal form Chalcocite - different
crystal form, darker, lighter in weight (5.5 - 5.8)
Tetrahedrite - harder (3 - 4), darker color, lighter in weight (4.6
- 5.1)
ENVIRONMENT:
It is found in medium and low-temperature ore veins,
in igneous and sedimentary rocks and disseminated through sediments.
Open cavities are frequent in these types of environment. So crystals
are common and well developed.
CRYSTAL DESCRIPTION:
Galena can show combinations of several forms of the cubic system along
with the octahedron and combinations of the two. Some cubic crystals
have their edges cut by the partial octahedral growth, some octahedral
crystals have their points flattened by cubic growth. Dodecahedral growths
may also be partially found in octahedral or cubic-octahedral crystals,
resulting in interesting shapes. Spinel twinning is possible forming
flattened crystals. Galena is also found in massive and granular form
TESTS:
Fuses on charcoal, with yellow coating around the bead, and can be reduced
to lead. Makes cloudy solution in nitric acid, with sulfur and lead
sulfate separating out.
LOCALITIES:
Galena is a very common mineral and occurs in numerous localities.
We will highlight just a few of the more notable ones. England has numerous
localities. Galena along with beautiful Fluorite occur in Alston Moor
and Weardale. Fine distorted crystals have been found in Black Forest
of Germany, and elsewhere in Europe. Naica, Chihuahua, Mexico produced
many interesting crystals, such as plates with twinned octahedrons.
The Joplin District of Missouri, Kansas, and Oklahoma is notable for
its crystals. Often formed in cubes, some times cubo-octahedrons with
octahedral growths on the faces. Enormous and well shaped crystals occur
in this area together with Sphalerite, Dolomite, and Marcasite. Some
of the famous areas in these localities include the Joplin area, Jasper
Co., Missouri; Galena, Treece, and Baxter Springs, Cherokee Co., Kansas;
and Picher, Ottawa Co., Oklahoma. We have some excellent Galena specimens
from the Sweetwater Mine, Reynolds Co., Missouri. Colorado has also
produced fine specimens Here in Idaho the Coeur d'Alene District is
a very important lead deposit, containing silver rich Galena. This area
is called the "Silver Valley" In California, much Galena occurs
at Darwin, Inyo Co., in the Blue Bell mine, San Bernardino Co., and
in the Jamestown mine, Tuolumne Co. Large amounts of Galena are mined
for lead production in south-central and southwestern Wisconsin.
USES:
Major ore of lead and silver, crystal forms make
excellent mineral specimens
FACTS & HISTORY:
It is believed that galena with flaky curving cleavage planes that
are irregular rather than plain and is often slightly tarnished. Is
likely to be higher in the silver content.
Galena is by far the greatest ore of lead. Galena is the most common
mineral containing lead, and contains mostly lead. Since the extraction
process is so simple, lead has been extracted from Galena since the
earliest times. Galena was also used in early radio devices.
Galena specimens tarnish when exposed to air becoming dull in luster.
The tarnish can be temporarily removed by scrubbing the specimen with
water and mild soap.
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