Washington, July 22 (IANS) A team of US geologists has found structurally bound hydroxyl groups in a mineral in a lunar rock returned to earth by the Apollo programme.

Geologists at the California Institute of Technology (Caltech), working with colleagues at the University of Tennessee, found the water in a calcium phosphate mineral, apatite, within a basalt collected from the moon's surface by the Apollo 14 astronauts, Xinhua reported.

To be precise, they didn't find "water" -- the molecule H2O. Rather, they found hydrogen in the form of a hydroxyl anion, OH-, bound in the apatite mineral lattice.

Their findings are published in this week's issue of the journal Nature.

The Caltech team analysed the lunar apatite for hydrogen, sulfur and chlorine using an ion microprobe, which is capable of analyzing mineral grains with sizes much smaller than the width of a human hair.

"The moon, which has generally been thought to be devoid of hydrous materials, has water," says John Eiler, professor of geochemistry at Caltech and a co-author on the paper.

"Hydroxide is a close chemical relative of water," explains George Rossman, Caltech's professor of mineralogy.

The lunar basalt sample in which the hydrogen was found had been collected by the Apollo 14 moon mission in 1971. The idea to focus the search for water on this particular sample was promoted by Larry Taylor, a professor at the University of Tennessee in Knoxville, who sent the samples to the Caltech scientists last year, the report said.