Simondium meteorite, Simondium, Drakenstein Local Municipality, Cape Winelands District Municipality, Western Cape, South Africai

Regional Level Types
Simondium meteorite	Meteorite Fall Location
Simondium	Hamlet
Drakenstein Local Municipality	Municipality
Cape Winelands District Municipality	District
Western Cape	Province
South Africa	Country

Stony-iron, Mesosiderite-A4
Find, 1907; 1.6 kg, several pieces

Two small apparent ' boulders' of unusual material were found buried 100 meters apart just below the surface in 'ironstone' gravel. Seeing exposed bright particles of metallic iron on the surface — and supposing them to be silver — the prospectors broke the boulders into small fragments. Two specimens were eventually analyzed at the British Museum and additional small fragments were collected later. While much of the iron (w. nickel) had been oxidized, the meteoritic nature of the mass was evident and the silicates were composed of readily observed orthopyroxene (~50%) and plagioclase ( ~ 40%). Olivine clasts, in contact with plagioclase, were abundant. Some unweathered Fe-Ni metal was present in small grains. Twinned plagioclase, usually indicative of shock, was common. Accessories such as apatite, augite, chromite, ilmenite, tridymite, and troilite were observed by Prior (1910, 1918). Prior, of course, classified Simondium as a mesosiderite and, using his observations alone, we could probably assign Simondium to its the more precise mesosiderite-A4 subtype under the modern classification scheme (abundance subclass A - high in plagioclase; petrologic type 4 — shocked matrix). Of course, a number of additional accessory minerals (listed below) and confirming associated features have been reported in the past several decades.

The complexities of mesosiderite mineralogy have occupied a number of people for the past century. It is still true that the orthopyroxene and other silicate clasts share many similarities with the largely Vesta-derived diogenites, but whether the silicate matrix and clasts of mesosiderites are actually Vesta-derived or not has not been demonstrated. More recent refined oxygen isotope systematic have apparently finally ruled out shared parent bodies for mesosiderites and pallasites, a hypothesis popular for several decades [Cf. Grady et al.,1915) for discussion and references].

Of the 37 mesosiderites that have been fully classified for both abundance and petrologic type at the 'Meteoritical Bulletin Database', Simondium is one of 4 meteorites classified as Mesosiderite-A4 [May 2015]. Major specimens have been held at the Museum of Natural History (London) and King William's Town Museum (South Africa) [~700 g and ~500 g, resp., as of 2000].

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References