regolith – the loose rock on the surface, resting on bedrock
This, from the newspaper, is modified for brevity.

President Bush wants to go back to the moon by 2002, but Houston has a problem: an acute shortage of fake moon dirt, called "lunar regolith simulant".

Lunar soil is nothing like the dirt found on Earth. The gritty talcum-powder-like soil is made up largely of glass, which forms when tiny meteorites hit the moon's surface and melt its mineral-rich soil. Nothing prepared astronauts on the moon for the clinging dust that clogged into spacesuit crevices and scratched equipment when it was wiped off.

Caterpillar Inc. alone estimates that it will need two to four tons of fake moon soil to develop heavy machinery to move lunar soil.

I wonder if it's from the Greek rhegos 'rug, coverlet'?

Does 'rug' come from the same root?

Does 'rug' come from the same root?

Not seemingly. Greek rhegos is thought (by Chantraine) to derive from the verb rezo ;to tint, dye', and English rug is related to an Old Norse verb rugga 'to rock (a cradle)'.

quote:

Originally posted by jheem: I wonder if it's from the Greek rhegos 'rug, coverlet'?

Indeed. AHD and MW each give it as being from rhegos + lith stone. But they render that the former as meaning 'blanket'. So we get a nice image of a blanket over the earth or moon.

(MW seems to have the notion that the -lith is an english suffix. But its from the greek, I gather.)

Well, a coverlet is close to a blanket, yes? Greek lithos 'stone'.