Desert Diary
September 10, 2003

Geology/Fool's Gold

 

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Gold! Or just a minute--is it really, or are we playing the fool? Many an amateur has had an adrenaline spike as the sparkle of gold shows in a rock outcrop or gleams from the bed of a mountain stream. And most often, that same amateur has been condescendingly informed that it's only fool's gold.

So what is fool's gold? The widespread mineral pyrite. For the more chemically gifted, iron sulfide, FeS₂. If indeed it were gold, the price of that precious metal would drop precipitously, for pyrite is common and widespread in metamorphic, igneous, and sedimentary rocks. It's often treasured by collectors for its varied crystals or for fossil bones or shells replaced by pyrite. That it is a brassy yellow with a metallic luster is what fools the uninitiated, but there's a simple test to avoid leaving yourself open to derision. Real gold is soft, easily scratched by a steel blade, while pyrite is hard. But sometimes, fool's gold isn't so foolish, for some deposits contain enough real gold to make mining it worthwhile.

Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.

Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.

References

Web Resources

Picture from Amethyst Galleries.