Category: Meteorite Primer & Guide

When people think they have found a meteoriteWork in progress. A solid natural object reaching a planet’s surface from interplanetary space. Solid portion of a meteoroid that survives its fall to Earth, or some other body. Meteorites are classified as stony meteorites, iron meteorites, and stony-iron meteorites. These groups are further divided according to their mineralogy and Click on Term to Read More, 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 ablationGradual removal of the successive surface layers of a material through various processes. • The gradual removal and loss of meteoritic material by heating and vaporization as the meteoroid experiences frictional melting during its passage through the atmosphere. The resulting plasma ablates the meteor and, in cases where a meteor Click on Term to Read More or various types of terrestrial weathering and generally describe a voidHuge region of space that is unusually empty of galaxies. Voids are not entirely empty, but are underdense and contain far fewer bright galaxies than average. 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 troiliteBrass colored non-magnetic Fe sulfide, FeS, found in a variety of meteorites. 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 crustOutermost layer of a differentiated planet, asteroid or moon, usually consisting of silicate rock and extending no more than 10s of km from the surface. The term is also applied to icy bodies, in which case it is composed of ices, frozen gases, and accumulated meteoritic material. On Earth, the Click on Term to Read More during entry.

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

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 chondritesChondrites are the most common meteorites accounting for ~84% of falls. Chondrites are comprised mostly of Fe- and Mg-bearing silicate minerals (found in both chondrules and fine grained matrix), reduced Fe/Ni metal (found in various states like large blebs, small grains and/or even chondrule rims), and various refractory inclusions (such Click on Term to Read More. 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 = chondriteChondrites are the most common meteorites accounting for ~84% of falls. Chondrites are comprised mostly of Fe- and Mg-bearing silicate minerals (found in both chondrules and fine grained matrix), reduced Fe/Ni metal (found in various states like large blebs, small grains and/or even chondrule rims), and various refractory inclusions (such Click on Term to Read More group (H, L, LL, CM, CK, R, …)
Gx = first chondrite group
Gy = second chondrite group
Ta = first chondrite petrologic typeMeasure of the degree of aqueous alteration (Types 1 and 2) and thermal metamorphism (Types 3-6) experienced by a chondritic meteorite. Type 3 chondrites are further subdivided into 3.0 through 3.9 subtypes.
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 brecciaWork in Progress ... A rock that is a mechanical mixture of different minerals and/or rock fragments (clasts). A breccia may also be distinguished by the origin of its clasts: (monomict breccia: monogenetic or monolithologic, and polymict breccia: polygenetic or polylithologic). The proportions of these fragments within the unbrecciated material Click on Term to Read More 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

When a meteorHow long Sonic booms Of the several 10s of tons of cosmic material entering Earth's atmosphere each day, only about one ton reaches the surface. An object's chance of survival depends on its initial mass, speed and angle of entry, and friability (tendency to break up). Micrometeoroids radiate heat so Click on Term to Read More is of sufficient size, its impact will leave a craterBowl-like depression ("crater" means "cup" in Latin) on the surface of a planet, moon, or asteroid. Craters range in size from a few centimeters to over 1,000 km across, and are mostly caused by impact or by volcanic activity, though some are due to cryovolcanism. Click on Term to Read More 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 craterBest known and best preserved impact crater on Earth. The crater is named after Daniel Barringer and still owned by his family and also known as Meteor Crater, Coon Butte, and Canyon Diablo (www.barringercrater.com). Measuring 1.2 km across and 175 m deep, with a rim 45 m higher on average Click on Term to Read More (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.

A meteoriteWork in progress. A solid natural object reaching a planet’s surface from interplanetary space. Solid portion of a meteoroid that survives its fall to Earth, or some other body. Meteorites are classified as stony meteorites, iron meteorites, and stony-iron meteorites. These groups are further divided according to their mineralogy and Click on Term to Read More 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 meteorHow long Sonic booms Of the several 10s of tons of cosmic material entering Earth's atmosphere each day, only about one ton reaches the surface. An object's chance of survival depends on its initial mass, speed and angle of entry, and friability (tendency to break up). Micrometeoroids radiate heat so Click on Term to Read More experienced as it smashed through our atmosphere.

 

 

 

 

As meteors rarely develop into perfect stable cones and can still experience significant ablationGradual removal of the successive surface layers of a material through various processes. • The gradual removal and loss of meteoritic material by heating and vaporization as the meteoroid experiences frictional melting during its passage through the atmosphere. The resulting plasma ablates the meteor and, in cases where a meteor Click on Term to Read More 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.

 

 

 

 

 

 

 

 

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 AustraliteTektites found in Australia and are part of the Australasian Tektite Field, a region extending as far as Sri Lanka to the West, Tasmania Australia to the South, Philippines to the East and Southern China to the North. Australites were deposited 0.79 Ma ago by a massive impact that rained Click on Term to Read More flanged buttons.