The origin of quartz silt shouldn't be taken for granite.
Geologists interested in the life and times of ancient oceans have long assumed that tiny particles of quartz found in mudstone under former seas got there from sources on land, including granite, limestone, and sandstone.
That's a reasonable assumption, says geologist Jürgen Schieber of the University of Texas at Arlington. Only it's wrong, he contends. In the Aug. 31 Nature, a team led by Schieber shows that quartz silt may have instead emerged from dissolved skeletons of tiny organisms, radiolaria and diatoms, that lived 370 million years ago.
If quartz grains entered the ocean as geological detritus carried from land by rivers or wind, the mineral should be more abundant near prehistoric coastlines. It isn't, Sc