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 pulverized bedrock at ground zero.  The melted material cools quickly, and falls back to Earth in the form of impact splash glasses (aka tektites).  Tektites are principally composed of amorphous silica (SiO2).  Broken surfaces show a conchoidal fracture.  Tektites from different impact events are given different names.





Indochinites are black-colored, moderately common tektites from southeastern Asia that typically are subspherical to tear-drop shaped to dumb-bell shaped.  They are found throughout the Australasian Tektite Strewn Field (aka Indochinite Tektite Strewn Field).  This strewn field is huge - it's estimated to extend over 10% of Earth's surface.  Indochinites have been found from Madagascar to Tasmania to South China.  Samples from different geographic areas are often given different names (e.g., australites, thailandites, malaysianites, philippinites, billitonites, vietnamites), but they were all apparently formed by the same event.  The impact crater has never been identified (it's been buried or eroded away?), but is thought to be in the vicinity of northern Vietnam, based on tetktite abundance patterns.  The fusion age of indochinites has been reported to be about 700,000 years (656-755 ky).


Indochinite - large teardrop-shaped specimen (5.2 cm across) from unrecorded locality in Guangdong Province, South China.


Indochinite - nice dumbbell-shaped specimen (9.1 cm across) from Zhanjiang, Guangdong Province, South China.


Indochinite - broken chips from the interior of a specimen from South China.  Left: 1.7 cm across; right: 1.8 cm across.


Billitonites (= indochinites) from Billiton Island (aka Belitung Island), Indonesia.  (FMNH Me 2326, Field Museum of Natural History, Chicago, Illinois, USA)





Moldavite is probably the most distinctive impact splash glass in the world, owing 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.


Moldavite (2.5 cm tall), derived from >4 meters below the land surface, below the water table, which accounts for the pitting and the surficial dissolution network.  It comes from a pit near the town of Besednice, in the Moldau (Vltava) River Valley area, southern Jihocesky Region (far-southern Bohemia), far-southern Czech Republic.




Bediasites are black-colored impact splash glasses from southeastern Texas, USA.  They form part of the North American Tektite Field, produced during the Late Eocene (35 million years ago) by the Chesapeake Bay Impact event (eastern seaboard of USA).  Other tektites produced by this event include georgiaites and specimens recovered from Massachusetts, Cuba, Barbados, offshore New Jersey, and in the Pacific Basin.


Bediasites on public display at the meteorite museum at Odessa Impact Crater, Texas, USA.





Tektites called Libyan Desert Glasses are known from a large area in western Egypt's Libyan Desert.  These nearly pure silica glasses range in color from pale yellowish to yellowish-green to brownish.  Their surfaces have been sculpted by wind-blown sand abrasion.  Available age information indicates that these rocks formed during the mid-Oligocene (28.5 million years ago).  The responsible impact crater(s) have not been identified with certainty.


Libyan Desert Glass (4.0 cm across)


Libyan Desert Glass on public display at the meteorite museum at Odessa Impact Crater, Texas, USA.


Libyan Desert Glass on public display at the meteorite museum at Odessa Impact Crater, Texas, USA.



Some info. provided by Povenmire (2003 - Tektites, a Cosmic Enigma) and Billy Glass.




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