Pyrite and gold form under similar
conditions, and can even occur together in the
In fact, in some ore deposits, tiny amounts of
gold can occur as inclusions and substitutions
within the pyrite! This is important because even
though you might think gold is better for its
monetary value, pyrite can be an important clue
for finding gold deposits, as well as for use in
sulfur and sulfuric acid production. Sulfur
dioxide is commonly used as a reducing agent in
the paper industry. Pyrite crystals also have use
in ornamental jewelry and other commercial
Geologists can use density to distinguish between
pyrite and gold because gold has a specific
gravity of about 19.3 while the specific gravity
of pyrite is only about 5.
Specific gravity is the density of a substance
compared to water. So water has a specific
gravity of 1. Density is the degree of
compactness of a substance. That means that
gold molecules are extremely compact, so gold
is about four times heavier than pyrite. Even
if the gold is alloyed, or mixed, with other
metals, it will still be noticeably heavier than
However, I said that gold and pyrite can be found
together, so how will you tell them apart?
Geologists have a few more tests besides
These tests include:
1) Tarnish. Pyrite often has a tarnished,
or dull, surface, while gold maintains its bright,
2) Color. Pyrite is usually slightly
brassy, or oranger, in color, while gold is
typically a whitish yellow color.
3) Shape. Pyrite is typically angular,
or pointy, and often found as a cube (6-sided)
or octahedron (8-sided) shape. Gold can resemble a
shape similar to pyrite, but often has rounded
4) Striations. Pyrite frequently has very
fine, parallel lines across the surfaces, whereas
gold crystals do not.
If you don’t mind damaging the specimens a little,
two more useful tests are streak and hardness.
5) Streak. Streak determines the color of
the mineral if it were powdered. You can identify
the streak by scraping the mineral across unglazed
porcelain. Pyrite has a dark greenish-black
streak, while gold has a yellow streak.
6) Hardness. Hardness is how resistant to
breaking or damage the mineral is. Pyrite is a
hard mineral and can scratch a copper surface.
Meaning pyrite could scratch a penny. Gold,
however, is very soft. Gold cannot scratch a
penny. In fact, if you poked a small flake of
what appears to be gold with a needle, pyrite
might break while gold will bend around the
The density of gold is approximately 19
grams/ cubic centimeter, and the density of
pyrite is approximately 5 grams/ cubic
centimeter, so gold is almost four times as
dense as pyrite.
A geologist who wants to compare the density
of two samples could put each one in a
graduated cylinder full of water and see how
much the water level rises to determine the
volumes. Then they could measure the mass of each
sample with a balance. Dividing the mass of each
sample by its volume gives the density.
Other ways to tell the difference are
shape (pyrite often grows in small cubes,
while gold does not) or hardness (Pyrite
has a hardness of about 6, and gold has a hardness
of about 2 on Moh's scale).
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