grad ed ▁by ▁weather ing ▁more ▁quickly ▁than ▁others . ▁Some ▁meteor ites , ▁especially ▁iron ▁meteor ites , ▁may ▁have ▁been ▁collected ▁by ▁people ▁in ▁the ▁past ▁who ▁recognized ▁them ▁as ▁being ▁unusual ▁and / or ▁useful , ▁thereby ▁removing ▁them ▁from ▁the ▁scientific ▁record . ▁Many ▁meteor ites ▁fall ▁as ▁show ers ▁of ▁many ▁stones , ▁but ▁when ▁they ▁are ▁collected ▁long ▁after ▁the ▁event ▁it ▁may ▁be ▁difficult ▁to ▁tell ▁which ▁ones ▁were ▁part ▁of ▁the ▁same ▁fall . ▁Many ▁meteor ites ▁are ▁found ▁by ▁people ▁who ▁sell ▁meteor ites ... ▁valuable , ▁rare ▁types ▁become ▁known ▁to ▁science ▁quickly , ▁while ▁those ▁of ▁low ▁value ▁may ▁never ▁be ▁described . ▁ ▁There ▁have ▁been ▁many ▁attempts ▁to ▁correct ▁statistical ▁anal ys es ▁of ▁meteor ite ▁finds ▁for ▁some ▁of ▁these ▁effects , ▁especially ▁to ▁estimate ▁the ▁frequency ▁with ▁which ▁rare ▁meteor ite ▁types ▁fall . ▁ ▁For ▁example , ▁there ▁are ▁over ▁ 1 0 0 ▁known ▁lun ar ▁meteor ite ▁finds , ▁but ▁none ▁has ▁ever ▁been ▁observed ▁to ▁fall . ▁ ▁However , ▁for ▁abund ant ▁types , ▁meteor ite ▁fall ▁statistics ▁are ▁generally ▁preferred . ▁ ▁These ▁statistics ▁are ▁current ▁through ▁June ▁ 9 , ▁ 2 0 1 2 . ▁ ▁Statistics ▁by ▁material ▁ ▁For ▁most ▁meteor ite ▁falls , ▁even ▁those ▁that ▁occurred ▁long ▁ago ▁or ▁for ▁which ▁material ▁has ▁never ▁received ▁complete ▁scientific ▁character ization , ▁it ▁is ▁known ▁whether ▁the ▁object ▁was ▁a ▁stone , ▁st ony ▁iron , ▁or ▁iron