Do you know the name of the only stone that floats? What about how amethyst gets its purple color, or what the New York state fossil is? Anatomist Howard Evans can tell you.

These are the kinds of topics that Evans, professor emeritus of biomedical sciences in Cornell's College of Veterinary Medicine addresses in a biweekly series, "Natural History Show and Tell Talks," in Alice Cook House Seminar Room 106. His Nov. 18 talk was "Fossils, Rocks and Minerals." Evans, 88, who has been at Cornell since 1940 (except for three years in the U.S. Army), also presents such talks regularly at public schools in the area. Teachers choose from a list of possible subjects he offers.

When speaking at public schools, however, Evans is subject to time constraints. "I can't show this much," he said, indicating the wide array of specimens he brought to the Cook House, "because they only have about 45 minutes."

At the Nov. 18 talk, students had more than an hour to view Evans' specimens, which included fossilized wood, obsidian, kimberlite with diamonds trapped inside, a fossilized fish, a tooth of an Eohippus (an extinct genus of a three-toed horse the size of a dog), picture sandstone and a vial of liquid mercury.

Several of the specimens were more than they initially appeared. A nondescript rock turned out to be a dinosaur gizzard stone -- that is, a stone that had been swallowed by a dinosaur and left behind with its fossilized bones. Students were able to handle the object, which had once been inside a prehistoric creature and which most people would probably overlook.

"If you didn't know about these things, you wouldn't pick them up," Evans said, holding up a plain, spherical rock. Opening the split halves of the rock, he revealed an interior filled with quartz crystals.

Evans explained that these rocks, called geodes, were at one point filled with water. "The silicon dioxide was in solution," he said, "and crystallized out as it dried." This process created the crystals inside the geode. In rare cases, "if you pick them up and shake them, you can hear the water inside. That water is thousands of years old."

This was only a small sample of Evans's collection, which is he always enlarging. When he travels, he said, people who lift his luggage will often ask him, "Have you got rocks in there?" To which the reply is invariably, "Yes!"

Evans plans to hold one more meeting for the Cook House program this semester to discuss skulls, antlers and horns, though the date is yet to be determined.

And in case you were wondering: The only stone that floats is pumice; amethyst gets its purple color from the chromium in it; and the New York state fossil is Eurypterus remipes, a species of marine crustaceans. Although Evans' fossil specimens were small, other eurypterids could grow to as long as 6 feet, having, Evans said, "a claw as long as your arm."

Jenny Proctor '12 is a writer intern for the Cornell Chronicle.