They are mostly true felspar basalts, but a few contain nepheline in addition to the felspar.
1); in others it is scarce and the rocks resemble trachytes containing a little nepheline (trachytoid phonolites).
Leucite and nepheline lavas are here abundant.
Nepheline basalts and liparites occur at Dombe Grande.
Kaolin and muscovite are formed principally after felspar (and the felspars are the commonest minerals of all crystalline rocks); also from nepheline, leucite, scapolite and a variety of other rock-forming minerals.
Leucite and nepheline rocks have been found in various parts of the island, especially in the south-west.
His turquoise glazes are obtained by using barium carbonate mixed with soda, feldspar and nepheline syenite.
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