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Fool's
Gold
"Gold, I found gold!," you shout to your friends. You quickly imagine
all the things you are going to do with your newfound wealth. Then
reality sets in, and you are embarrassed to discover that you have
been tricked by the mineral pyrite, also known as fool's gold. Take
heart, you are not the first person (nor the last) to be fooled
by pyrite. Even Captain John Smith (of Pocahontas fame) mistakenly
sent an entire shipload of pyrite to London in the early 1600s,
while exploring the Chickahominy River for a waterway to the Pacific.
How can I tell the difference between gold
and pyrite (fool's gold)?
Pyrite crystals commonly
form pyritohedrons (twelve irregular five-sided faces) with striations
on the crystal faces.
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Visual clues -
- Color: Gold and pyrite
both have a brilliant metallic luster, but are different tones
of yellow. Gold is golden to silvery yellow, whereas pyrite is
a pale to medium brassy yellow that sometimes tarnishes.
- Shape: Gold usually occurs
in nuggets or very small flakes, sheets, and shapeless grains.
Small cubic and octahedral (two pyramids with bases joined) gold
crystals are very rare. Pyrite crystals commonly form cubes, octahedrons,
or pyritohedrons (twelve irregular, pentagonal or five-sided faces),
frequently with striations (parallel lines) on the crystal faces.
Pyrite can also occur as shapeless grains.
Physical tests -
- Hardness: Scratch the mineral
with the blade of a pocket knife. Rub off any loose powder to
see if the mineral has been scratched. Gold is much softer than
pyrite and can be cut. Pyrite cannot be scratched. (Beware - chalcopyrite
looks similar to pyrite, but is softer and can be scratched with
a knife. It is a very brassy yellow, often with a bronze or iridescent
tarnish.)
- Odor: Rub the mineral vigorously
with a hard object. Gold has no odor, but pyrite gives off a sulphurous
smell (like rotten eggs).
- Malleable: Strike the mineral
with a steel hammer. Gold will flatten or change shape without
breaking. Pyrite will give off sparks.
Good luck in your quest for gold
and don't be fooled by fool's gold!
 
 
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