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Difference Between Holes, Cavities, and Vesicles in Meteorites

When people think they have found a meteorite, much more often than not, what they found is actually a terrestrial rock, often referred to as a meteorwrong. These rocks come in all shapes, sizes, colors and textures, and sometimes include holes. In posting these specimens for review, they may be told that “meteorites do not have holes”. Though generally true, this statement misleading because a simple internet search will uncover images of actual meteorites with holes. This article is written to clarify this issue.

Though our definitions for holes and cavities differ somewhat from the dictionary definition, they are better descriptors than what is normally used to describe meteorites.

Holes can be caused by ablation or various types of terrestrial weathering and generally describe a void that extends all the way through a specimen.

Cavities can also be caused by ablation and in that case are called regmaglypts, or by the weathering of softer or more degradable material within the meteorites such as troilite in iron meteorites.

 

Vesicles are caused due due trapped gases expanding within the molten material/melt at its time of formation and are rarely bigger than a few millimeters, though in extremely rare cases one or two larger vesicles can by be larger. Vesicles inside meteorites do not occur due to its voyage through our atmosphere, though bubbles/vesicles can form on the outside crust during entry.

Ibitira eucrite meteorite with vesicles.
Tissint Martian shergottite with vesicles in shock melt veins. Image Credit: Mendy Ouzillou
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How to Start a Meteorite Collection

Michael Kelly:

My recommendation is you start up a catalog now keep track of important info on your collection when you bought it total weight total cost, details of why it interested you etc. if you keep at it it’s hard to “catch up” on details later. The little nuances you might forget in a piece in 3 decades or 400 pieces later

Greg Stone

Please categorize any and all new specimens collections – keep records, I am truly sorry I didn’t when I was purchasing prior 10-12 years ago. Now I just have a mess of things I am now trying to rectify

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Classification Punctuation for Chondrites

The Meteoritical Bulletin is filled with incredible meteorite-related information. However, even the most experienced collector might be puzzled when evaluating a classification and trying to understand the various punctuation used by the Nomenclature Committee. For example, do you understand the difference between an L/LL3 and an L(LL3)? Please note that the punctuation only covers chondrites. There is little carryover into the achondrites, irons and stony-irons, and within these other groups, there are discrepancies.

Meaning Behind Punctuation in Chondrite Classifications:

G = chondrite group (H, L, LL, CM, CK, R, …)
Gx = first chondrite group
Gy = second chondrite group
Ta = first chondrite petrologic type
Tb = second chondrite petrologic type

  • Parentheses
    • Gx(Gy) means a chondrite either of Group X or less likely Group Y. Example: L(LL3)
  • Slash
    • Gx/Gy means a chondrite of either Group X or Group Y. Example: L/LL3
    • One exception is Isheyevo, CH/CBb, where the slash means a chondrite that is transitional between the CH group and the CB group.
  • Dash
    • GxTa-Tb means a chondrite comprised of a breccia whose clasts/components range from petrologic Type A to Type B. Example: CK3-6
    • If A and B are one level apart, then means a chondrite of Type A and Type B. Example: R3-4
    • If the dash comes at the end of the group or type, then what follows provides added information. Examples: -melt breccia, -an, -ung
  • Period
    • Used to denote a chondrite’s petrological subtype and only associated with Type 3 (unequilibrated), Type 2 and presumably Type 1. Example: CO3.0
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Craters Formed by Meteor Impacts

When a meteor is of sufficient size, its impact will leave a crater and in rare cases, meteorites will be found in and/or around the crater. Here is a list of craters and their associated meteorites:

  1. Agoudal
  2. Barringer crater (Canyon Diablo)
  3. Boxhole
  4. Campo del Cielo
  5. Carancas
  6. Dalgaranga
  7. Haviland
  8. Henbury
  9. Kallijarv
  10. Monturaqui
  11. Morasko
  12. Morokeweng
  13. Odessa
  14. Santa Fe
  15. Sikhote-Alin
  16. Veevers
  17. Wabar
  18. Whitecourt
  19. Wolf Creek

List is courtesy of Rob Keeton.

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Orientation and Oriented Meteorites

Modified from Image Source: Rasslava / iStock / Getty Images Plus

A meteorite develops orientation when it experiences a period of stable flight through Earth’s atmosphere and is gradually further ablated into an increasingly more stable and aerodynamic shape (cone or shield). The resulting meteorite can show evidence of flow lines, roll-over lipping and regmaglypts. Though features of orientation can be seen on any meteorite type, iron meteorites (e.g Sikhote Alin) best preserve the faintest and most distinct features that the meteor experienced as it smashed through our atmosphere.

 

 

 

 

Study of fluid dynamics helps researchers uncover the mystery of oriented meteorites using aluminum cones falling in water. Image Modified from the Source: shanghai.nyu.edu

As meteors rarely develop into perfect stable cones and can still experience significant ablation during inversion, tumbling, and gliding trajectories, the characteristics associated with meteorite orientation can appear somewhat subjective for the uninitiated. However, there are clear objective identifying characteristics associated with oriented meteorites that make them prized by collectors. One or more of the features listed below can be found on all oriented meteorites:

  1. Conical or shield shape where the leading surface or apex experiences the highest temperature and pressure and is ablated into a rounded shape, and the trailing surface is more or less flat (can be slightly concave, convex or a combination of both).
  2. Flow lines indicating a consistent direction of travel and, emanating from the apex of meteorite and leading back towards trailing surface, or flowlines can also occur in certain areas below the leading surface. The most dramatic flowlines occur in a radial pattern as seen below on the Lafayette meteorite.
  3. Roll-over rim/lip develops when the ablating/melting material begins to flow over onto the back side of a meteor or from a protuberance on the leading surface. The material that has lipped over can also have flow lines and even appear frothy with tiny bubbles in the lipped region. Some meteorites can even experience double lipping indicating that they experienced stable flight in two directions.
  4. Regmaglypts or fluting/feathering (long regmaglypts) indicating large scale ablation in a consistent direction radiating from the apex. In rare cases, the regmaglypts can occur in a radial pattern as well.
  5. Spattering of small molten droplets (called travelers by some collectors) that adhered on the meteorite’s trailing surface or behind a feature like a raised surface or protuberance. This feature is typically seen on iron meteorites though large droplets have been seen on the backside of oriented stony meteorites. Evidence of this feature does not by itself mean the meteorite is oriented, though it can be associated with it.

A word of caution: Meteorites that don’t display flowlines (2), lipping (3), or regmaglypts (4) can be mislabeled as oriented. Just because a meteorite is shaped like a pyramid or sits on a flat edge does not mean it is oriented. Some meteorites are clearly oriented, but if there are doubts, ask an expert.

Beautiful radial flowlines displayed in the Lafayette meteorite (Nakhlite). Image Source & Credit: AMNH & Chip Clark
Stunning fluted regmaglypts in the Chrysanthemum meteorite. Photo Credit: Emaan Baqai/UCLA Daily Bruin senior staff
Sikhote Alin with complete rollover lip/rim. Note lip that extends far into back surface on left and sputtering of material top right. SkyFall Collection.
Karakol fell May 9, 1840 in Kazakhstan and is an excellent example of a cone shaped oriented meteorite. Measured q = 50o. Image Source: www.meteorites.ru

 

 

 

 

 

 

 

 

Note that rotational spin plays an important role in the shaping and stability of a meteor but is not discussed in detail here. Also, the plasticity of tektites during flight leads to amazing orientation effects as seen in Australite flanged buttons.