Here is a specimen with GOLDEN PYRITE SUN on
a BLACK SLATE MATRIX
It is from Sparta, in Randolph Co., Illinois.
(Pyrite is also known as FOOL'S GOLD.) The
disc is shaped like a SUN, a flat, round form
of pyrite that is named for its resemblance to the
sun. The discs are found in narrow seams of SLATE
(about 320 MILLION YEARS OLD), between seams
of coal in the mines near Sparta, IL. There are
several theories about the origin of these
formations. One is that they are pyritized
REPLACEMENTS of an earlier FOSSIL CREATURE.
Another is that they are the flattened result of a
PYRITE CRYSTAL spread out under HEAT AND
PRESSURE in the seams of slate.
Pyrite is the classic "Fool's Gold". There are other
shiny brassy yellow minerals, but pyrite is by far
the most common and the most often mistaken for
gold. Whether it is the golden look or something
else, pyrite is a favorite among rock collectors. It
can have a beautiful luster and interesting
crystals. It is so common in the earth's crust that
it is found in almost every possible environment,
hence it has a vast number of forms and varieties.
Bravoite is the name given to a nickel-rich iron
sulfide. It is closely related to pyrite but
contains up to 20% nickel. Some mineral books treat
it as a variety of pyrite.
Pyrite is a polymorph of marcasite, which means that
it has the same chemistry, FeS2, as marcasite; but a
different structure and therefore different symmetry
and crystal shapes. Pyrite is difficult to
distinguish from marcasite when a lack of clear
indicators exists.
Pyrite's structure is analogous to galena's
structure with a formula of PbS. Galena though has a
higher symmetry. The difference between the two
structures is that the single sulfur of galena is
replaced by a pair of sulfurs in pyrite. The sulfur
pair are covalently bonded together in essentially
an elemental bond. This pair disrupts the four fold
symmetry that a single atom of sulfur would have
preserved and thus gives pyrite a lower symmetry
than galena.
Although pyrite is common and contains a high
percentage of iron, it has never been used as a
significant source of iron. Iron oxides such as
hematite and magnetite, are the primary iron ores.
Pyrite is not as ecomonical as these ores possibly
due to their tendency to form larger concentrations
of more easily mined material. Pyrite would be a
potential source of iron if these ores should become
scarce.
Pyrite has been mined for its
sulfur content though. During WWII, sulfur was in
demand as a strategic chemical and North American
native sulfur mines were drying up. A sulfide
deposit near Ducktown Tenn. was found to be able to
mine pyrite and other sulfides such as pyrrhotite
and pentlandite and produce the needed sulfur as
well as iron and other metals. The sulfur was used
in the production of sulfuric acid, an important
chemical for industrial purposes. Now most sulfur
production comes from H2S gas recovered from natural
gas wells.
