The Piancaldoli meteorite: A forgotten primitive LL3.10 ordinary chondrite

The Piancaldoli ordinary chondrite fell in northern Italy on August 10th 1968 and was collected the same day. Preliminary studies led to its classification as an LL 3.4 unequilibrated ordinary chondrite. The recent developments of new classification procedures have prompted us to design a multitechnique study for re-determining its mineralogical, petrographic, spectroscopic and chemical and isotopic features. Our results reveal that Piancaldoli is less altered than previously reported and should be reclassified as an LL 3.10 unequilibrated ordinary chondrite. In combination with the findings of previous studies, our data confirm the reliability of the use of Cr content variability in type II ferroan chondrule olivine as a proxy of thermal metamorphism. The Cr indicator gives consistent estimation with those inferred from Raman spectroscopy measurements and magnetic properties. The high hydrogen content of Piancaldoli also attests that Piancaldoli experienced minimal thermal metamorphism. Our results also imply that the bulk deuterium enrichment in deuterium observed in Piancaldoli (LL 3.10), Bishunpur (LL 3.15) and Semarkona (LL 3.00) is a specific signature of the most primitive unequilibrated LL chondrites. Based on our results, we propose that Piancaldoli corresponds to the second least altered fall unequilibrated ordinary chondrite after Semarkona. This shows that meteorite collections worldwide are fundamental resources for studying the formation conditions and evolution our solar system.