The emerald is the birthstone for May, and yesterday an unpolished emerald crystal was installed permanently in the Birthstones exhibit of the Wertz Gallery at the Carnegie Museum of Natural History in Oakland.

The crystal is 5.8 centimeters (about 2.3 inches) long and was found in 2003 in an emerald mine in Alexander County, N.C., the only emerald-producing district in the United States.

"This emerald possesses everything we want for public view," said Marc Wilson, head of the gallery's minerals section. "Out of the thousands of emeralds that this mine has produced, the museum's emerald is easily in the top 10 percent ever found."

For security reasons, museum officials would not disclose the value of the mineral crystal. For museum hours and admission prices, call 412-622-3131 or visit carnegiemnh.org.

-- LaMont Jones