Lafayette (stone) Martian meteorite, Lafayette, Tippecanoe County, Indiana, USAi

Regional Level Types
Lafayette (stone) Martian meteorite	Meteorite Fall Location
Lafayette	City
Tippecanoe County	County
Indiana	State
USA	Country

Nakhlite (martian clinopyroxenite)
Find: 1931; 800 g, an intact stone

A small, relatively fresh meteorite was found lying in the drawers of Purdue University's Geological Department. The fusion crust of its 'front side' was completely covered with well-defined, oriented flow lines rarely seen even in witnessed meteorite falls. After recognition as a meteorite, some inquiries were initiated concerning the now recognized geological visitor. It is quite possible that the stone had been recovered almost immediately after it had fallen in the mud of a small lake. However, no written records were taken when the stone arrived at the university — and efforts to locate the finder were unsuccessful. Quite apart from the uncertain circumstances of its recovery, the extraordinary unusual and unique geochemistry and mineralogy of Lafayette (stone) were not recognized for several decades. Mason (1962) identified Lafayette (stone) as a pyroxene-rich meteorite similar to Nakhla. However, the suggestion that Lafayette was 'merely' a misplaced specimen of Nakhlite was still receiving some currency in the 1985 Catalogue of Meteorites. Lafayette is indeed quite similar to Nakhlite as both meteorites are pyroxenites containing significant amounts of accessory olivine. Lafayette itself consists of pyroxene (~75 vol%) [mostly augite], somewhat unevenly distributed olivine (~15 vol%), and a more complex matrix or mesostasis which includes some late crystallizing phases and some hydrated phases. Augite is found as euhedral prisms while olivine is found as anhedral grains. Several of the accessory phases (minor silicates, opaques, phosphates) are not unexpected in cumulate rocks — and, once Lafayette was recognized as a martian cumulate, the phases now seem quite unexceptional. Lafayette's hydrated phases, however, remain exceptional. One expects weathered meteorites to contain hydrated phases altered by interactions with the atmosphere and surface waters which penetrate all meteorite finds. Textural evidence, however, suggests that almost all of the hydrated phases are preterrestrial — small inclusions protected by surrounding pyroxene and olivine grains which had themselves remain largely intact. In addition, studies of deuterium isotopes in the hydrated phases indicate that most or even almost all of their deuterium is Mars-derived. Lafayette, it appears, contains as much Mars-derived water of hydration as any other Martian meteorite — perhaps more.

The Lafayette (stone) meteorite has been one of the best indicators that the rocks that now lie on and beneath the deserts of Mars have been exposed to water well beyond the expectations of many scientists and laypersons alike. The reported crystallization ages of nakhlites are ~1.3 Ga. Several nakhlites and 2 chassignites have cosmic ray exposure ages of ~10 Ma suggesting that they may well have been ejected from Mars in a single impact event.

As of June 2015, Lafayette (stone) is the 3rd most massive of only 15 nakhlites listed in the Meteoritical Bulletin Database [several specimens are apparently paired]. Most of the mass, including a 602 g specimen, is at the U.S. National Museum (Smithsonian).

The exact location of the fall is unknown.

What's in a name? The 'Lafayette (stone)' is to be distinguished from the lost 'Lafayette (iron)' meteorite reported to have been found in Colorado, USA.

Other Regions, Features and Areas containing this locality

References