[meteorite-list] Re: H vs. L survival
From: Robert Verish <bolidechaser_at_meteoritecentral.com>
Date: Thu Apr 22 09:48:12 2004 Message-ID: <20011017214730.7339.qmail_at_web10402.mail.yahoo.com> Hello Rob, Rodrigo, Don, and List: I think it only fair, since Rob used data from my study area at Lucerne Valley, that I use his data from another study area to make a stronger case for metallic iron content having MINIMAL bearing on the survivability of a chondritic stone from weathering. Rob's data is still unpublished, but the main point is that, within one "area of high concentration", he has found a number of VERY weathered chondrites that are nearly devoid of "metallic Ni-iron", yet the stones are still quite competent - with a solid interior and still retaining a relatively well preserved exterior. Granted, the hematite from the oxidized metal may actually be holding the stone together, but the point is that chemical weathering alone will not have a bearing on a chondritic stones survivability. During the very complex process of meteorite weathering, it is the degree of energy in an environment (mechanical weathering) that will be the determining factor in a meteorites survivability. In this case, the amount of "metallic Ni-iron" has little bearing on the matter. To be specific, here is Rob's data: H6, S1, W4, Fa 19.4 +/- 0.1 H6, S2, W6, Fa 19.0 +/- 0.3 L6, S4, W3, Fa 25.1 +/- 0.3 L6, S3, W5, Fa 25.0 +/- 0.5 L6, S3, W6, Fa 25.4 +/- 0.2 L4, S2, W2, Fa 24.3 +/- 0.2 H6, S3, W2, Fa 18.5 +/- 0.7 Within one "area of high concentration" where Rob has found 9 chondritic stones representing ~7 meteorite falls (3ea. H6 & 4ea. L4-L6), there are an equal number of H and L of W4-W6. In this particular case, the metal grains in the H6's appeared to have been much finer-grained than those in the L's. When those grains were oxided, the resultant finer pores facilitated "hematite cementing" of the matrix, making for a more weather resistant stone. Granted, the smaller metal grains oxided faster than the larger metal grains in the L-chondrites, but this was more than compensated by the greater degree of "hematite cementation". As I said earlier, terrestrial weathering is a very complex process. But my hunch is, if you went to all the bother to rank all the contributing factors to this process, that the POROSITY of a meteorites interior will have a greater role in the rate of weathering, probably by a factor of 10, more so than the proportion of its metal grains. I could go on and on about weathering, but the bottom line is that what I'm observing in the field and in the interiors of these meteorites is that there is no over-riding factor for preferential weathering based upon H vs. L chemistry. If, for a given area, all that has been found are L-chondrites, then all this means is that you haven't found the H-chondrites yet. ;-) Bob V. ------------------- Original Message ------------------ [meteorite-list] H vs. L survival From: Matson, Robert ROBERT.D.MATSON_at_saic.com Date: Tue, 16 Oct 2001 19:06:19 -0700 Hi Rodrigo, > [Do]The Meteorites found in the areas of high density > that you cite have low proportion of Metal? Well, let's see: Lucerne: L6, LL4, H6, H4, L6, H6, L5, LL6, L6 and one ordinary chondrite (type not determined). 3 H's, 4 L's and 2 LL's. A pretty good spread. Roach: H5, LL6, L5, L6 Other undisclosed locations also seem to have a good mix of L's and H's. Time may indeed favor the L's survival over the H's in some locations, but so far the finds in the desert southwest don't show an obvious trend of L's over H's. Cheers, Rob __________________________________________________ Do You Yahoo!? Make a great connection at Yahoo! Personals. http://personals.yahoo.com Received on Wed 17 Oct 2001 05:47:30 PM PDT |
StumbleUpon del.icio.us Yahoo MyWeb |