xOoids : Small (< 2 mm), spheroidal, layered sedimentary grains, usually composed of calcium carbonate, but sometimes made up of iron- or phosphate-based minerals.
In the spring of 2010, the eruption of a volcano called Eyjafjallajökull in Iceland cancelled many flights in Europe. Eyjafjallajökull is a glaciovolcano, which means it's a volcano that is covered by...Read more