The Perils of Meteorite Type Collecting - A Guide
This article is directed at the silent newbie or befuddled beginner who is sorting through the confusing groups of meteorite types and trying to find their way around the world of space rocks.
Many new collectors often want one of each type of meteorite. Many veteran collectors abandon this pursuit because the task is quite daunting. So when you hear talk about "type collecting", or building a "type collection", what exactly does that mean?
I hope the following brief article will answer those questions, or at least point the reader in the right general direction. Note, I gleaned much of this type information from David Weir's authoritative website "Meteorite Studies" and from the Meteoritical Bulletin. I do not claim that this list is 100% complete or without error, so if the reader spots an error or omission, please reply and correct it.
I started out collecting meteorites with a small sample of NWA 4293 - an ordinary high iron chondrite of the H6 type. It was about the size of a dog-food kibble and it looked like one. But I was instantly hooked, and I wanted to have one each of the different types of meteorite. This is known as "type collecting" or building a "type collection".
The danger of type collecting is that the various petrologic types are subdivided into various grades according to metamorphism.
For example, take the H chondrite group that my NWA 4293 sample belonged to.
There are H3 chondrites, H4 chondrites, H5 chondrites, and H6 chondrites. Did I really need one each of these subtypes? Well, it depends on how deep a collector wants to go down the rabbit hole. There are distinct differences between the various H types.
The number attached to each is more than just a simple weathering grade or shock grade. It represents a progession in the H-chondrite family from least altered to most altered. H3 chondrites are loaded with chondrules, H4 have some chondrules, H5 has few chondrules, and H6 has virtually no visible chondrules. A new grade of H7 has been added as well. So, a collector could simply have a single Hx chondrite and say that the H-chondrites are represented. Or, the collector could have one each of the different subtypes from 3 to 7.
Another peril is the changing of nomenclature. For example, the K-subgroup of carbonaceous chondrites was only recognized and designated in 1990. Up until then, Karoonda was considered a CV4 meteorite of the Vigarano family. Now Karoonda is recognized as distinctly different type of carbonaceous chondrite, so it was made into it's own group. Now we have CK4, CK5, and CK6 meteorites - all represent a progression in metamorphism and have visible (and chemical) differences from other grades. There are standout members of each subgroup, so where does one draw the line?
Should the collector acquire a sample of Karoonda and be done with it? Or should one go out and track down CK4, CK5 and CK6 meteorites? Again, it depends on how extensive and exhaustive a collector wants to be with their type collection. Budget will also play a role as well, because an exhaustive type collection is an expensive project.
Lastly, one must consider the ungrouped meteorites. These are oddball meteorites that do not neatly fit into the pre-existing meteorite types. There are ungrouped chondrites, ungrouped achondrites, and ungrouped irons. No type collection can overlook these meteorites because some of them are types unto themselves with unique qualities.
For those who want to build a definitive and complete type collection, here is a list of every known type and subtype of meteorite. This list was culled from other sources, including David Weir's authoritative "Meteorite Studies" website linked at the end of this post.
Carbonaceous Chondrites :
CM2 (subdivided into CM2.0 to CM2.6)
CO3 (Ornans) (subdivided into CO3.03 to CO3.7)
CV (Vigarano) (also CV2 and CV3)
CK (Karoonda) (CK4, CK5, CK6)
CR (Renazzo) (CR1, CR2, CR3)
C ungrouped (Tagish Lake, others)
Ordinary Chondrites :
Rumuruti R3 (subdivided into R3.5-6 to R3.9)
LL (subdivided into LL3.0 to LL3.9)
LL impact melt
LL transitional (L/LL3 to L/LL6)
L (subdivided into L3.0 to L3.9)
L impact melt
H/L transitional (H/L3 to H/L6 IMB, H/L3.6 to H/L3-4)
H (subdivided into H3.0 to H3.9)
H impact melt
ungrouped ordinary chondrites
Enstatite Chondrites :
EL (EL3 to EL7)
EL impact melt
EH (EH3 to EH7)
EH impact melt
ungrouped enstatite chondrites
Meta-chondrites (M-CV, M-CR, M-H, M-LL)
Primitive Chondrites :
ungrouped primitive chondrites
Howardite (subdivided into fragmental breccia and regolith breccia)
Eucrite (monomict and polymict with each having subclasses)
Diogenite (monomict and polymict)
Ureilite (monomict and polymict)
Martian achondrites :
Pyroxene-phyric basaltic shergottite
Olivine-phyric basaltic shergottite
Olivine-orthopyroxene-phyric basaltic shergottite
Pyroxene-peridotitic (Wehrlitic) shergottite
Basaltic Breccia ("Black Beauty" NWA 7034 and pairings)
Orthopyroxenite (ALH 84001)
Lunar Achondrites :
Impact melt breccia
Other Achondrites :
Angrites (Plutonic and Basaltic)
ungrouped achondrites (Ibitira, Pasamonte, etc)
Pallasites (Main Group, Eagle Station group, Pyroxene group)
Pallasite-am (anomalous, PMG-am, PMG-as)
Iron meteorites :
Note, iron meteorites are a can of worms. I will only focus on the main chemical groups, and not the various grouplets and sub-types of each main chemical group. Also note that many of these types include silicated varities. Listing all of the known sub-types of irons would require a LONG list resembling a flow-chart.
I think that is all of them - as currently recognized by the Meteoritical Society Nomenclature Committee. If anyone can think of some I missed, please contact me and I will add them to the list.
David Weir's Meteorite Studies website - http://www.meteoritestudies.com/