Surprising because, contrary to what the first reviews (which are usually the ones that remain, and that I transmitted) said, the restingolites are not the result of a mixture of an acid magma with other poor in SiO2, or the incorporation into the magma of preexisting volcanic rocks from the sides of the island of El Hierro. Nothing further, the whitish inner (which had been associated with a silica-rich magma, rhyolite type, which is typically known as pumice) do not contain any of the usual volcanic minerals or associated to volcanism. Amphibole, pyroxene, feldspar and olivine are absent in the samples collected. Instead we find wollastonite (mineral which forms only in the high temperature metamorphism of the calcium carbonate or calcite) and jasper and quartz grains, all of microscopic size.
These magmatic rock fragments that are not incorporated into a magma are called "xenoliths" (from the Greek ξένος, Xenos, "strange" and λίθος, lithos, "stone" strange stone). They are quite common and very useful for geologists engaged in understanding how igneous rocks are formed. But in this case, the restingolite has a peculiarity, as it can float for hours, much like the true volcanic rock pumice. This is because the amount of gas that encloses (in the case of restingolite, the black lava crust make the fragment almos hermetically closed), and this feature has earned for the rock its own right to name it as a new rock type, the Xeno-pumice.