Hello Frank and list, fcressy wrote: > The rock is a howardite if it contains greater than 10% > orthopyroxene and a polymict eucrite if it has less than 10%.
Frank I don't believe this interpretation of the rule is correct. From what I gather, a polymict eucrite contains more than 90% eucrite components, but the remaining 10% may consist of anything else, including a small, less than 10%, component of orthopyroxene, together with a small, perhaps 5%, component of your dark material along with accessory minerals. However, given the specific composition you proposed ... "hypothetically, if NWA 1109 has an orthopyroxene (diogenite) component of 8% plus another 5% of chondritic material" ... then I would say it would be a howardite because it is inconsistent with the definition of a polymict eucrite or diogenite, which specifies that it must contain greater than 90% of a single component, and that would be impossible since 12% is accounted for. I would also imagine the case could arise where part of a meteorite is a howardite and part is a polymict eucrite. I would think that the additional method of distinguishing them apart, zoned versus unzoned pyroxenes in basaltic clasts, would be helpful in this case. David ______________________________________________ Meteorite-list mailing list [EMAIL PROTECTED] http://www.pairlist.net/mailman/listinfo/meteorite-list
