The Палласитес are a class of stony–iron meteorite. They are relatively rare, and can be distinguished by the presence of large olivine crystal inclusions in the ferro-nickel matrix. These crystals represent mantle and core material from differentiated planetesimals, which were destroyed by violent collisions during the early formation of the Solar System.

Structure and composition

It consists of centimetre-sized olivine crystals of peridot quality in an iron-nickel matrix. Coarser metal areas develop Widmanstätten patterns upon etching. Minor constituents are schreibersite, troilite, chromite, pyroxenes, and phosphates (whitlockite, stanfieldite, farringtonite, and merrillite).

Classification and subgroups

Using the oxygen isotopic composition, meteoric iron composition and silicate composition pallasites are divided into 4 subgroups:

Origin

Pallasites were once thought to originate at the core-mantle boundary of differentiated asteroids that were subsequently shattered through impacts. An alternative recent hypothesis is that they are impact-generated mixtures of core and mantle materials. This hypothesis is supported by isotopic analysis indicating admixture of material from multiple planetesimals.

History

A common error is to associate their name with the asteroid 2 Pallas but their actual name is after the German naturalist Peter Pallas (1741–1811), who studied in 1772 a specimen found earlier near Krasnoyarsk in the mountains of Siberia that had a mass of 680 kg. The Krasnoyarsk mass described by Pallas in 1776 was one of the examples used by E.F.F. Chladni in the 1790s to demonstrate the reality of meteorite falls on the Earth, which most scientists at his time considered as fairytales. This rock mass was dissimilar to all rocks or ores found in this area (and the large piece could not have been accidentally transported to the find site), but its content of native metal was similar to other finds known from completely different areas.

Pallasite falls

Pallasites are a rare type of meteorite. Only 61 are known to date, including 10 from Antarctica, with four being observed falls. The following four falls are in chronological order:

Notable pallasite finds

Although pallasites are a rare meteorite type, enough pallasite material is found in museums and meteorite collections and is available for research. This is due to several large finds, some of which yielded more than a metric ton. The following are the largest finds: