Micros and Macros from New England Meteoritical ServicesMeteorite Classification and the Pricing of Micro and Macro Meteorites
Meteorites are pieces of other solar system bodies. The majority originate from asteroids shattered in collisions with other asteroids. In a few cases, they have come from the moon and, presumably, comets and the planet Mars (Zagami and Nakhla).
There are three types of meteorites: Stone, Stony-Iron, and Iron, with many sub-groups within each type.
Stone meteorites consist of two groups: chondrites and achondrites.
Most chondrites have remained unchanged since their formation. They included carbonaceous chondrites and the rare enstatite chondrites (E chondrites). Almost all chondrites contain chondrules - small, glasseous, spherical inclusions that formed during the solar nebula. Some carbonaceous chondrites are believed to have cometary origin and E chondrites may have formed within the orbit of Mercury.
Chondrites are further grouped by H, L, and LL classifications - primarily indicating iron content - and by the numbers 1 to 7. H chondrites have the highest amount of iron - about 27 percent total iron by weight with 12 to 20 percent of the iron in the uncombined metal state. L chondrites contain lower iron amounts, roughly 23 percent but the amount of free iron metal is only 5 to 10 percent. The interiors contain fewer visible metal inclusions or flakes, than H chondrites. Olivine is still the abundant mineral but hypersthene, the iron-rich orthopyroxene, is also found. LL chondrites represent "low total iron" and "low metal" content. Sometimes referred to as amphoterites they contain only 20 percent total iron with only 2 percent iron by weight.
The numbers following the H and L classifications are petrologic designations indicating the degree of chondrule alteration by heating. Well-defined, slightly altered chondrules have a petrologic grade of 3. A Higher number of 5, 6, or 7 indicates an increased level of metamorphism caused by heating thus making the chondrules less distinct. Chondrites, the most abundant of meteorites, were formed during or shortly after the birth of the Sun and have remained unaltered in the 4.56 billion years since. They remain the principal source of evidence concerning the origin and early history of our solar system. Some, like the Allende meteorite contain remnants, or interstellar grains, of a star that lived out its life in our locality and exploded as a supernova. It was from this gaseous, molecular debris that the proto-solar nebula formed.
A few meteorites (e.g. Murchison) have been found to contain water and amino acids, compounds of carbon, hydrogen, and oxygen. These may be samples of the material that started our oceans and atmosphere, and perhaps provided the material from which life evolved.
Achondrites are "high-energy" meteorites in the sense that they appear to have been chondritic before being altered by an immense heating or impact event at an asteroidal or planetary level. They are much rarer than chondrites and include the Eucrites (asteroid Vesta), SNC's (Martian origin), Howardites, Brachinites, Aubrites, Ureilites, and Diogenites. Additionally, there are further groupings such as Acapulcoites, Winonaites, and Lodranites.
Mesosiderites and Pallasites are the two main groups of the Stony-Iron type. Mesosiderites consist of broken angular fragments of mantle rock that impacted with another body. Pallasites are some of the most attractive of all meteorites. One leading theory of their formation argues for a core-mantle boundary origin.
Iron meteorites are pieces of the shattered core of differentiated asteroids and contain varying amounts of nickel. Defining the many classifications of iron meteorites are beyond the scope of this page and we refer you to our educational site at www.meteorlab.com for further information. Briefly however, they are basically composed of three groups: Hexahedrites which contain 4.5 to 6.5 percent nickel, Octahedrites with 6.5 to 13 percent, and Ataxites with nickel amounts from 16 to 20 percent. Hexahedrites contain the nickel-iron mineral kamacite. These meteorites are generally large cubic crystals of kamacite. Internally, hexahedrites are rather featureless except for occasional fine parallel lines called Neuman Lines and other inclusions.
The octahedrites consist of a striking intergrowth of the two nickel-iron minerals kamacite and taenite. This crystallization of metal occurs during extraordinarily slow cooling rates - around 2 to 4 degrees per million years. When polished and etched they reveal the structure known as the Widmanstatten Pattern. Ataxites, which means "without structure", are rare, nickel-rich meteorites. They consist almost entirely of the mineral taenite.
The cost of any meteorite is generally dependent upon rarity and weight. In many instances, only a small amount of a particular meteorite is recovered. If this particular meteorite is of a rare classification, its cost will be greater than many pieces of a more common type. More often than not, however, many meteorites, both common and rare, are simply not available to collectors and educators at any price!
In offering micro and macro-sized specimens, NEMS has worked diligently to stabilize the availability of many meteorites in a similar manner to the way Ward's Scientific stabilized the availability of minerals to the educational community for over forty years. Micro and Macro meteorites vary in size and are not sold by gram weight. Their cost is determined by rarity, abundance, and the degree of laboratory preparation necessary to offer the best possible specimen at a reasonable price.
While it is always more cost-effective to buy larger specimens, 50 or 100 grams or more, the cost is usually prohibitive or specimens that large are not available. In assessing the gram/price ratio of micros and macros, the cost per gram may be higher but one is able to acquire representative samples of a variety of Micro and Macro meteorites at an affordable price.