Cosmogenic sediment components
When an object such as a comet, asteroid, or large meteorite hits the Earth, the heat and pressure of the impact melt part of the rock and sediment at the impact site. Some of the melt is thrown from the crater with other debris and solidifies in flight to glass. Large blobs of impact glass are called tektites. If tektites are small enough to be seen only with a microscope, they are called microtektites.
Tektites and microtektites are usual spherical but can also be shaped like teardrops, dumbbells, or ovals. They often have a pitted or grooved surface. A single impact can create a widespread marker bed of tektites in seafloor sediments.
The image opposite is a microtektite. The scale bar is 0.05 mm.
Rothwell, 1989, Fig. 120.