No real chance for volcanism out here. That's the thing. Counts metamorphic and igneous right out... but there's no traditional sediment to make any other kind of stone. The way it would come into existence on this planet... not even sure we'd know how that could change the properties.

[He let the scan continue aand frowned.]

The idea it's just floating is... damned weird. Wait... no... maybe the conditions could allow for volcanic heat to rise at some point in the past. So it might actually be similar to pumice. Damnit, my kingdom for a xenogeologist!