They are mainly composed of magnesioferrite
, spinelloid, and lepidocrocite.
The magnetic residues of sample 75-503, consist primarily of chromite and magnesioferrite, which are highly enriched in Ir, Ni and Cr (Table 1, cf.
At these localities the spherules were associated with dark, clay-rich spherules full of quench crystals of magnesioferrite spinel, and enriched in iridium opposite the Ir concentration of the K/T boundary clay itself (33 and 2 ppb, respectively).
The composition of larger lobate grains shows their pertinence to titaniferous magnetite with a higher content of ulvospinel molecule ([Fe.sub.2]Ti[O.sub.4]) and low contents of Mn, Mg, Al, thus forming very low proportions of jacobsite, magnesioferrite
, and hercynite, respectively, and sometimes V.
, like ludwigite, has been found as microscopic inclusions in native arsenic from the Bor pit.
The iron oxide will go readily into solution in the magnesia lining forming magnesioferrite
or magnesiowustite, depending upon the partial pressure of the available oxygen.