PSEUDOFOSSILS - "Fossils" That Aren't!

Several mineral growths look for all the world like fossils.

- JIM BRACE-THOMPSON

Some even fooled the best experts of the day. Take, for example, tiny rod-like structures in a Martian meteorite that top NASA scientists interpreted in 1996 as fossilized microbes from another planet. The finding even led to a dramatic speech by then-President Bill Clinton. But those “microbes” turned out to be structures left by non-biological mineral growths. They just coincidentally resembled filament-like forms of some living bacteria here on Earth.

FOSSIL OR PSEUDOFOSSIL?

Remains of organic life forms older than 10,000 years are called fossils. They can take the form of bones, teeth, scales, shells, carbonized remains of leaves, chemical traces, molds or casts. Mineral growths or rock formations that look deceptively like fossils, but are not, are called pseudofossils. (“Pseudo” is from a Greek word meaning false or deceiving.) Such objects are inorganic. That is, they were never alive. They formed from natural geochemical processes within the Earth and—like those Martian microbes—resemble fossils by pure coincidence.

FLOWERS THAT AREN'T

At a gem show, a friend asked, “Did you see that petrified flower?” Being a fossil collector, I hurried to the exhibit he pointed out. What I found was no fossil. It was a chrysanthemum stone, or a mineral that forms in a flowerlike pattern. In this instance, it was a radiating cluster of white andalusite crystals in a black matrix. In other varieties of chrysanthemum stones, the “flower petals” may be composed of celestite, feldspar, calcite, or aragonite, and the matrix may be gray or black limestone, dolomite, basalt, or porphyry. All entirely inorganic.