Bitterroot Gem & Mineral Club

Bitterroot Gem & Mineral Club of Montana

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Common Tektites

Bolides & Impact-Craters, & their Debris (Meteorites & Tektites) Continued... By Wayne Farley

Rocks: Millions of rocks have fallen to the earth over geological time from the breakup of bolides in the atmosphere. Most of these have disintegrated from geological and geochemical possesses. The survivors that have been found are cataloged by “The Meteoritical Society”, as well as many others. The Meteoritical Society is a non-profit scholarly organization founded in 1933 to promote research and education in planetary science with emphasis on studies of meteorites and other extraterrestrial materials, including samples from space missions that further our understanding of the origin and history of the solar system. The membership of the society boasts over 1000 scientists and amateur enthusiasts from over 40 countries who are interested in a wide range of planetary science. Members' interests include meteorites, cosmic dust, asteroids and comets, natural satellites, planets, impacts, and the origins of the Solar System. The Meteoritical Society is the organization that records all known meteorites in its Meteoritical Bulletin. The Society also publishes one of the world's leading planetary science journals, Meteoritics and Planetary Science. The Society organizes annual meetings and workshops. It also helps encourage and support young planetary scientists world-wide. The Meteoritical Society is supported by the subscriptions of its members and generous contributions to its endowment funds

The Meteoritical Society website provides information to its members on news and events, and provides resources to encourage the advancement of planetary sciences. (Ref-4,   

Glass (Tektites) (from Greek τηκτός tēktós, "molten") are gravel-sized bodies composed of black, green, brown or gray natural glass formed from terrestrial debris ejected during meteorite impacts. The term was coined by Austrian geologist Franz Eduard Suess (1867–1941), son of Eduard Suess.[1] They generally range in size from millimeters to centimeters. Millimeter-scale tektites are known as microtektites. (Wikipedia, 02/18)    

Tektites somewhat resemble obsidian volcanic glass, but describes the differences in the paragraph below. The biggest difference is that tektites contain about 40 parts per million of water, whereas, obsidian contains about 4000 parts per million. Microtektites have been found on the moon by our moon astronauts, and this has strengthened the theory that volcanoes on the moon are the source of earth tektites. (Povenmire, Ref-6) “Tektites are small pieces of natural glass which have entered the Earth’s atmosphere at least once. The origin of Tektites is controversial but all have a cosmic connection where obsidian does not. They superficially resemble obsidian but are much dryer with a water content of usually about 40 parts per million. Tektites are wetter than Moon rocks or lunar meteorites but much drier than terrestrial obsidian. Tektites usually contain reduced alkali (K20 and Na20). Tektites are composed of the oxides of metals and have the inverse ratio of the greater amount of SiO2, the less the amount Al203. Tektites usually have a range of SiO2 of between 60 and 84 percent and more than 10 percent Al203. Since Tektites are glass they exhibit the typical concoidal fracture. Tektites resemble some sedimentary rocks like loess and subgreywacke in chemical composition. Their index of refraction is approximately 1.48 and their specific gravity is approximately 2.4. Tektites have a Moh’s scale of hardness of approximately 6.5 or slightly less than that of pure quartz or SiO2. Tektites are somewhat translucent with colors varying light green, drab olive green to very dark brown. The color is determined by the amount and state of the iron oxide. Tektites do not contain crystals or microliths and all tektites by definition contain lechaterlierite, a form of SiO2. Tektites are usually very homogenous and seldom show inclusions or bubbles, except the Layered or Muong Nong-type. Tektites have a high melting point because many of their volatiles evaporated off during reentry and are usually more brittle than other natural glasses. Tektites have four basic forms. These are splash forms like dumbbells or teardrops. They also occur in the layered or Muong Nong-type. Some will show aerodynamic or fluididal shaping and will also occur as microtektites which are smaller than 1.0 mm in diameter. Tektites show no relationship to the local rocks where they fell. Tektites fall in large groups of similar composition and age, and these areas are called strewn fields. Meteorites are not found associated with tektites, strewn fields or connate craters. 

 Tektites are characterized by

1.  a fairly homogeneous composition; 

2.  an extremely low content of water and other volatiles

3.  an abundance of lechatelierite

4.  a general lack of microscopic crystals known as microlites and chemical relation to the local bedrock or local sediments; their distribution within geographically extensive strewn fields.

  “Tektites (tectites) are members of a large group of impact glasses, formed by the collision of a meteorite on the Earth’s surface and the subsequent melting of surrounding rocks. The most famous tectites used as gemstones are moldavites from southern Bohemia in the Czech Republic. These were formed by a meteorite’s impact in the Ries crater in southern Germany 14.7 million years ago, about 500 km from their occurrence (V. Bouška, Moldavites: The Czech Tektites, Stylizace, Prague, 1994). Moldavites are popular for their pleasant green color, enigmatic origin, and interesting etched texture. They are used in jewelry, in either faceted or natural form. The price of moldavite has risen in the last few years, and as a logical consequence imitations have become more widespread. In fact, moldavite imitations are nothing new. Faceted moldavites were very popular in Czech jewelry during the second half of the 19th century, often with Czech garnets (chrome pyropes) or small river pearls. Their use diminished in the beginning of the 20th century when imitations made from green bottle glass began to appear.