Iron meteorites are the type most people think of when they hear the word. However, only about 10% of the meteorites that reach Earth are Irons. The rest are stone or stony-irons. Iron meteorites are thought to originate from the metallic cores of planets or planetoids, or perhaps from the explosion of a supernova. Iron is a major by-product of stellar fusion. The core of the Earth is thought to be nickel-iron. In fact, iron meteorites also contain some portion of nickel. Iron and nickel are related metals, and only one other element, cobalt, separates them on the periodic table of elements.
The amount of nickel is what determines a meteorite's classification within the iron family. The combination of these two metals makes for an extremely hard material, well-suited for survival in deep space, and even the more harsh erosive environment here on Earth. The metals melted in deep space, and were then crystallized in the near absolute-zero, high vacuum void of outer space, resulting in a crystalline structure unlike any found on Earth.
The crystalline structure is revealed when a freshly cut or ground section of meteorite is etched with a mild acid. The Widmanstatten pattern is the unmistakable signature of an iron meteorite. It is rated in various classifications from fine to coarse, depending on the size of the crystal structure. Some meteorites with high nickel content will show no such pattern, however, nor do stone meteorites.
Most of the time the pattern is broken up by inclusions of various types, made up of silicates, sulphur, carbon, and other material. If inclusions dominate extensively, the meteorite is reclassified.
Silicated irons have a large percentage of inclusions. So much so that the metal pattern inside is made up of clumps and veins of metal and other material. They are lighter than pure Irons, and because the different materials have varying burn characteristics, the surface texture is more interesting, with more "thumbprints"- concave depressions resembling craters or hollows.
Stony-Irons are rare and among the most beautiful and precious of meteorites. It is unclear when a silicated iron becomes a Stony-Iron. There are two kinds: mesosiderites, and pallasites. Mesosiderites are a conglomeration of stone and metal, while pallasites, for our money the most beautiful meteorite that exists, is nickel-iron interspersed with large crystals of olivine, a yellow-green igneous rock, translucent in thin slices or polished tones.
Stone meteorites are the most common type, but also the most precious and valuable because they are hard to distinguish from Earth rocks. They also erode more quickly than the durable irons and stony-irons. Although these are the most varied in structure and content, they are divided up into two main types, chondrites and achondrites Chondrites contain chondrules, microscopic to marble-sized spherical globs of silicates from the earliest solar nebula, sometimes pre-dating even planetary formation!
Chondritic material accreted into planetesimals, which were then bombarded by other bodies, resulting in the breakup and destruction of the planetesimal. If the parent planetesimal grew large enough, the pressure and temperature melted and re-crystallized the chondritic material,resulting in achondrites, the rarest form of meteorite. Achondritic meteorites can be pieces of other mature planets or moons, which were ejected by a large impact, and may have traveled the solar system for eons before landing on Earth. Such is the case with the Antarctic Mars meteorite alleged to contain fossils of Martian microbes.
-
Meteorites are named for the locale, region, or nearby
-
town in which the "fall"occurred.
-
-
Although the fusion crust may be warm or hot
-
immediately after impact, the inside of the meteorite is still
-
deep frozen from eons in cold space.
-
-
For years, the standard price for meteoritic material was
-
$1/lb. Now, many meteorites are worth as much as gold!
-
-
Falls that are witnessed yield higher-value meteorites, no matter what classification.
-
-
Meteorite falls are located in "strewn fields", elongated footprints that vary due to impact angle, airbursts, and speed.
-
-
Many meteorites are found by farmers plowing their fields, or prospectors, looking for precious gems and minerals.
-
-
Meteorites have been used by unsuspecting finders as blacksmith anvils, dog bowls, or to prop up machinery or autos.
-
-
Meteorites often contain minerals not found on Earth.
-
-
Meteorite falls often knock out power and anything electrical in the area. This may be due to the EMP, or electromagnetic pulse, of the fast-moving meteor.
 |
The largest meteorite discovered in Antarctica is about 2 feet by 2 feet by 1.5 feet. Due to its size it was not able to be thawed in the 100% nitrogen atmosphere and therefore the ice inside melted. The liquid water dissolved minerals inside the meteorite, and when it evaporated, white salts were left on the surface of the meteorite. NASA Lyndon B. Johnson Space center |
|
