Moldavite from the Miocene of Bohemia. (2.5 centimeters tall)

Large & small impacts have affected Earth since its formation 4.55 billion years ago. Compared with the intensely pitted and cratered Moon, Earth has relatively few preserved impact craters, because they have been destroyed by water & glacial erosion. Impact events are accompanied by tremendous amounts of heat, resulting in melting of much of the ejected pulverized bedrock at ground zero. The melted material cools quickly, and falls back to Earth in the form of impact splash glasses (a.k.a. tektites). Tektites are principally composed of amorphous silica (SiO2). Broken surfaces show a conchoidal fracture. Tektites from different impact events are given different names.

Moldavite is probably the most distinctive impact splash glass in the world, due to its pleasant green color. Like other impact splash glasses, moldavite is amorphous SiO2 with minor Al, Ca, Fe, K, and Na. Moldavite formed ~14.5-14.8 million years ago, during the mid-Miocene, in association with the Ries Impact Crater, located in Bavaria, Germany.

The specimen shown above is derived from >4 meters below the land surface, below the water table, which accounts for the pitting and the surficial dissolution network.