[meteorite-list] The 100th Bulletin Now Out

[Jeff Grossman]

These tildes have been used before.  Here is a rundown of all the 
special notation you may see in chondrite classifications.

For petrologic types:

~ (tilde) means that the petrologic type was not determined very 
precisely -- maybe just with a visual guess.  H~5 is an H chondrite that 
is approximately petrologic type 5.

/ (slash) means indeterminate between the two numbers, and therefore you 
can never have H4/6... only H4/5 or H5/6.  I see that there are a few 
4/6 meteorites in the bulletin, and these were due to editorial 
oversights: they are mostly 4-6 breccias (or errors).  I'll fix some of 
these soon.

- (hyphen) means the chondrite is a breccia with components spanning the 
given range.  An H3-5 chondrite has components that are type 3, type 5, 
and possible (but not necessarily) type 4.

For chondrite groups:

/ (slash) is a problem, and can have two meanings.  It can either mean 
indeterminate, as it does for petrologic types, or it can mean 
transitional or intermediate. There is no way to tell which is meant.  I 
was going to propose a new notation for real transitional meteorites 
like Bjurböle, which currently is written L/LL4:  the new notation would 
be L^LL4, with the caret indicating its real place in the middle.  
Perhaps we'll see this appear one day.

Parentheses indicate uncertainty.  For highly unequilibrated chondrites, 
it is nearly impossible to discern the difference between L and LL 
groups, and so they may be called L(LL)3, meaning "probably L3, but 
possibly LL3.  In fact, unless somebody did bulk chemistry and O 
isotopes to find out the real answer, probably every very low petrologic 
type OC with large chondrites should be really called L(LL) or LL(L).

Note that there is NO existing notation for polymict breccias, say one 
with an L host meteorite and CM clasts, so you never see something like 
L-CM.  Think what a mess Kaidun or Almahatta Sitta classifications would 
be if you used hyphens in the same way we do for petrologic types!

Note also that not all classifiers have clearly understood the 
difference between - and / for petrologic types.  Some of the 
classifications in the literature almost certainly have these reversed.  
Most of these get caught by NomCom, but not all.

Jeff

On 6/22/2011 3:44 PM, Thunder Stone wrote:
> List:
>
> I was looking a the lastest submissions in the Bulletin and noticed some OC's in the 100th Bulletin with the class:
> H~6, H~5, L~5... and so on.  Apperently the "tilde symbol" means that the meteorite has an "approximate petrologic type."
> So, what is the diiference between H5, H approximately 5, H 4-6, and H 4/6?
>
> Seems a little odd to me, but maybe there is an important reason for it.
>
> Greg S  		 	   		
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