Madison Gem and Mineral Club presentation by Tom Scharff Ð Tuesday, February 26, 2008
Selected Meteorite Vocabulary

Ablation - vaporization due to atmospheric heating

Accretion - accumulation of dust and gases into larger bodies in the solar system.

Achondrite - stony meteorite type lacking chondrules. these have undergone melting and recrystallization on or within the parent bodies. because differentiation is an igneous process, these are igneous rocks or breccias (consisting of angular fragments) of igneous rocks.

Bolide - a fiery object streaking across the sky

Chondrite -stony type of meteorite which contain large amounts of carbon, water and other volatile compounds and believed to be the most primitive condensed matter in the solar nebula. some of these, the carbonaceous chondrites, contain volatile organic compounds, as well as water. the presence of these chemicals is evidence that these meteorites have not been heated above 200¡ celsius.

Chondrule- small, glasslike, round body found in stony meteorites. it is believed to have crystallized from molten droplets present during the initial stages of condensation of the solar nebula. 

Fall-  meteorite which was seen to fall from the sky and which was tracked down successfully. A fall also refers to meteorites in a specific area, considered to have fallen at the same time.

Find- meteorite which was found on the ground unrelated to any sighting, due to the finder recognizing it to be clearly identifiable as being of nonterrestrial origin. Meteorites found on top of the snow in Antarctica are also classified as finds. Some finds come from rooftops and the like. A few have come from cars and the street.

Fusion crust - glassy coating caused by falling through the atmosphere

Impact crater - geological depressions resulting from large comets, asteroids, or meteorites striking the surface. The Earth is still geologically active, so older craters tend to get erased. Mercury, mars, and the moon are stable, so they have a much more pockmarked appearance from millions of years of impacts!

Impact glass- silica-rich glassy material likely to have been caused as a result of meteoritic impact

Meteor- a Òshooting starÓ in the sky caused by a meteoroid entering the earthÕs atmosphere

Meteorite- a portion of a meteoroid which survives its fall through the atmosphere, and impact with the ground

Meteoritics- the study of meteorites

Pallasite- a class of stony-iron meteorite containing olivine crystals in a nickel-iron matrix

Meteoroid-  a piece of debris in the solar system, between the size of a grain of sand and a boulder

Naming- meteorites identified since 1981 are usually named for the nearest town or geographical feature to the location of the strewn field. exceptions to this include dense collection areas like Antarctica, northwest Africa, south and western Australia.

Parent body - the asteroid or planetary body from which a meteorite originated. besides asteroids, the moon and mars are known to be parent bodies of meteorites found on earth.

Regmaglypts-  shallow ÒthumbprintÓ pits on a meteoriteÕs surface caused by the earthÕs atmosphere

Strewn field- an area where meteorites have landed on the ground is a strewn field. on earth, strewn fields are often created when a meteor breaks up in the atmosphere, scattering pieces over a wide area, usually elliptical in shape.

Shocked - having undergone thermal alteration (metamorphism) on its parent asteroid, such as melting and recrystallization

Tektite - glassy material which fell to earth, probably from the moon, but possibly originating from earth. Tektites show evidence of being heated twice. The first process melted the entire rock, the second only melted the outside, due to friction upon re-entry to the earthÕs atmosphere

Widmanstatten lines - long nickel-iron crystals consisting of interleaved kamacite and taenite bands called lamellae. They become visible when nickel-iron meteorites are cut, polished, and etched with acid because taenite is resistant to the acid. Wider bands indicate higher iron content, finer bands mean more nickel is present, since nickel bonds more easily than iron. They were discovered in 1808 by the director of the imperial porcelain works in Vienna and named after him.