Washington, Dec 8 (IANS): US space agency NASA's Mars Rover has found bright veins of a mineral, possibly gypsum, deposited by water on the red planet.

"This stuff is a fairly pure chemical deposit that formed in place right where we see it," said Steve Squyres of Cornell University, principal investigator for Mars Rover Opportunity.

"That can't be said for other gypsum seen on Mars or for other water-related minerals Opportunity has found. It's not uncommon on Earth, but on Mars, it's the kind of thing that makes geologists jump out of their chairs," added Squyres, according to a NASA statement.

The vein examined most closely by Opportunity is about the width of a human thumb, 16 to 20 inches long, and protrudes slightly higher than the bedrock on either side of it.

Observations by the durable rover reveal this vein and others like it within an apron surrounding a segment of the rim of Endeavour Crater.

None like it were seen within 33 km of crater-pocked plains that Opportunity explored for 90 months before it reached Endeavour, nor in the higher ground of the rim.

Last month, researchers used the Microscopic Imager and Alpha Particle X-ray Spectrometer on the rover's arm and multiple filters of the Panoramic Camera on the rover's mast to examine the vein, which is informally named "Homestake".

The spectrometer identified plentiful calcium and sulphur, in a ratio pointing to relatively pure calcium sulphate.

"It is a mystery where the gypsum sand on northern Mars comes from," said Opportunity science-team member Benton Clark of the Space Science Institute in Boulder, Colorado.

"At Homestake, we see the mineral right where it formed. It will be important to see if there are deposits like this in other areas of Mars," added Clark.