The crystal mountains, which were found on the Moon by India’s Chandrayaan-1 probe, are a sign that a roiling ocean of magma once engulfed the rocky body of our satellite, say scientists.

And heavy, iron-bearing minerals are thought to have sunk through this magma to form the moon”s mantle, while lighter, iron-poor minerals called plagioclases should have crystallised and floated to the surface.

But it has been difficult to find direct evidence of the Moon’s primordial crystalline crust, as it was likely jumbled by meteoroid impacts and paved over by lava flows early in the Moon’s history.

Until recently, the only evidence came from lunar samples collected at a few sites by the Apollo astronauts.

However, last year, Japan’s Kaguya probe spotted patches of the stuff inside a number of craters.

And now, Chandrayaan-1, which orbited the Moon for almost 10 months until it failed in August, seems to have found the mother lode – vast outcrops of plagioclase crystal along a mountain range inside the moon”s 930-kilometre-wide Orientale basin.

Lava has resurfaced less of Orientale than other craters of its size.

In 1994, the US orbiter Clementine found regions inside Orientale that seemed to be virtually iron-free, hinting at plagioclase, but Chandrayaan-1 was able to detect the light absorbed by the crystal itself.

It found that the rock containing the crystal spans at least 40 kilometres and is quite pure – less than 5 per cent of it is composed of iron-rich minerals.

This is purer than a number of Apollo samples, which until now have been the primary source of information on the Moon’s ancient crust.

“This is a game-changer. We now have to rethink a lot of lunar science; issues such as the way the crust originally floated over the denser melt of the magma ocean [and] the extent to which the crust was jumbled by large impacts,” New Scientist quoted Paul Warren of the University of California, Los Angeles, as saying.

Finding widespread, pure plagioclase suggests a more global process behind moon’s formation.

“It really pretty much ties up the magma ocean part of the story,” said Carle Pieters of Brown University in Providence, Rhode Island.

He presented the Chandrayaan-1 results at the American Geophysical Union meeting in December in San Francisco.

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