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and in ancient and recent marine sediments has been investigated.
Experiments were performed reproducing in laboratory the same processes undergone by the cosmic dust during its flight through the atmosphere.
Spherules similar in size, shape, chemical and mineralogieal characteristics to the natural ones have been obtained. It has been tested that hollow spherules can be also produced in the high atmosphere.
The bubble formed inside some black magnetic spherules by the decrease of solubility of oxygen at the melting point can be sometimes ejected from the rear side of the spherule producing secondary particles less than 10 pim is size.
The volcanic origin of black magnetic spherules has been excluded.
In fact ferromagnetic volcanic particulate matter present mineralogic,
chemical and structural characteristics different from that of black magnetic spherules.
Also the use of some parameters is suggested to discriminate industrial
ferromagnetic spherules from black magnetic spherules of extraterrestrial origin.
Samples from sediments old enough to exclude industrial contamination
allow to calculate the earth accretion in cosmic dust.
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