Meteorite Classification - Traditional Classification Scheme

Traditional Classification Scheme

Meteorites are often divided into three overall categories based on whether they are dominantly composed of rocky material (stony meteorites), metallic material (iron meteorites), or mixtures (stony–iron meteorites). These categories have been in use since at least the early 19th century but do not have much genetic significance; they are simply a traditional and convenient way of grouping specimens. In fact, the term "stony iron" is a misnomer as currently used. One group of chondrites (CB) has over 50% metal by volume and contains meteorites that were called stony irons until their affinities with chondrites were recognized. Some iron meteorites also contain many silicate inclusions but are rarely described as stony irons.

Nevertheless, these three categories sit at the top of the most widely used meteorite classification system. Stony meteorites are then traditionally divided into two other categories: chondrites (groups of meteorites that have undergone little change since their parent bodies originally formed and are characterized by the presence of chondrules), and achondrites (groups of meteorites that have a complex origin involving asteroidal or planetary differentiation). The iron meteorites were traditionally divided into objects with similar internal structures (octahedrites, hexahedrites, and ataxites), but these terms are now used for purely descriptive purposes and have given way to modern chemical groups. Stony–iron meteorites have always been divided into pallasites (which are now known to comprise several distinct groups) and mesosiderites (a textural term that is also synonymous with the name of a modern group).

Below is a representation of how the meteorite groups fit into the more traditional classification hierarchy:

  • I) Stony meteorites
    • Chondrites
      • Carbonaceous chondrite class
        • CI chondrite (Ivuna-like) group
        • CM-CO chondrite (mini-chondrule) clan
          • CM chondrite (Mighei-like) group
          • CO chondrite (Ornans-like) group
        • CV-CK chondrite clan
          • CV chondrite (Vigarano-like) group
            • CV-oxA chondrite (oxidized, Allende-like) subgroup
            • CV-oxB chondrite (oxidized, Bali-like) subgroup
            • CV-red chondrite (reduced) subgroup
          • CK chondrite (Karoonda-like) group
        • CR chondrite clan
          • CR chondrite (Renazzo-like) group
          • CH chondrite (Allan Hills 85085-like) group
          • CB chondrite (Bencubbin-like) group
            • CBa chondrite subgroup
            • CBb chondrite subgroup
      • Ordinary chondrite class
        • H chondrite group
        • L chondrite group
        • LL chondrite group
      • Enstatite chondrite class
        • EH chondrite group
        • EL chondrite group
      • Other chondrite groups, not in one of the major classes
        • R chondrite (Rumuruti-like) group
        • K chondrite (Kakangari-like) grouplet (a grouplet is a provisional group with <5 members)
    • Achondrites
      • Primitive achondrites
        • Acapulcoite group
        • Lodranite group
        • Winonaite group
      • Asteroidal achondrites
        • HED meteorite clan (possibly from asteroid 4 Vesta, also called basaltic achondrites)
          • Howardite group
          • Eucrite group
          • Diogenite group
        • Angrite group
        • Aubrite group (enstatite achondrites)
        • Ureilite group
        • Brachinite group
      • Lunar meteorite group
      • Martian meteorite group (sometimes called "SNC meteorites")
        • Shergottites
        • Nakhlites
        • Chassignites
        • Other Martian meteorites, e.g., ALH84001

  • II) Stony–iron meteorites
    • Pallasites
      • Main group pallasites
      • Eagle station pallasite grouplet
      • Pyroxene pallasite grouplet
    • Mesosiderite group

  • III) Iron meteorites
    • Magmatic iron meteorite groups
      • IC iron meteorite group
      • IIAB iron meteorite group
      • IIC iron meteorite group
      • IID iron meteorite group
      • IIF iron meteorite group
      • IIG iron meteorite group
      • IIIAB iron meteorite group
      • IIIE iron meteorite group
      • IIIF iron meteorite group
      • IVA iron meteorite group
      • IVB iron meteorite group
    • Non-magmatic or primitive iron meteorite groups
      • IAB iron meteorite "complex" or clan (formerly groups IAB and IIICD)
        • IAB main group
        • Udei Station grouplet
        • Pitts grouplet
        • sLL (low Au, Low Ni) subgroup
        • sLM (low Au, Medium Ni) subgroup
        • sLH (low Au, high Ni) subgroup
        • sHL (high Au, Low Ni) subgroup
        • sHH (high Au, high Ni) subgroup
      • IIE iron meteorite group

Read more about this topic:  Meteorite Classification

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