SMYRNA, Tenn. — A Smyrna resident has discovered that the rock she used as a doorstop for 15 years is a 450-million-year-old fossil.

The Daily News Journal reports (http://on.dnj.com/W4j819) Betty LeMaster found the 10-pound rock when she was cleaning up her property. It propped open the door between her washroom and den until she became curious about it while watching a television program called "America Unearthed."

Alan Brown, a geosciences instructor at Middle Tennessee State University, said LeMaster's rock is a fossilized coral.

The rough exterior is dotted with dime-sized chambers that appear to have starburst-like protrusions. Those protrusions are tentacles, which were likely used to anchor down in order to avoid being eaten by fish.

LeMaster said she is happy to finally learn about her rock, calling it "a piece of history."

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Information from: The Daily News Journal, http://www.dnj.com