Enstatite mineral residues

In Nature, an additional mineral, nierite (Si3N4), was found in the perchloric acid-resistant residues of primitive meteorites (ordinary chondrites [29] and enstatite chondrites [30, 31]) [32]. This mineral was seen to occur in lathe-shaped grains that were 2 pm x 0.4 pm in size. An inspection of the mineral by using selected area electron diffraction (SAED) showed the d-spacings of nierite to be comparable to those of synthetic a-Si3N4. The unit-cell parameters of nierite, as calculated from measured d-spadngs, were a = 0.774 0.002 nm, c = 0.561 0.002 nm, while the calculated density was 3.11 gcm [33]. 

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