TEKTITES
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.
INDOCHINITE
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
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.
BEDIASITE
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.
LIBYAN
DESERT GLASS
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.