(1) The synthetic material is highly transparent and contains few inclusions.

(2) Cleavage closely approximates to that of a natural mica, but differs in detail.

(3) The material appears to be largely polycrystalline consisting in parts of almost parallel plates.

(4) As distinct from the natural mica the synthetic material has numerous chemically active centres which attack silver.

(5) Most of the material shows no birefringence on the cleavage surfaces, but a local birefringent area has been found.

It may be concluded that the synthetic material is much more free from inclusions than natural phlogopite. In this respect it closely resembles a muscovite. Crystallographically, however, it is less perfectly formed than a natural mica, although the differences as listed above are not such as to make a serious distinction. In cleavage and structural characteristics, as in homogeneity, the synthetic material is inferior to a good grade of muscovite, but superior to a natural phlogopite.