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The analyses show the composition of Cornish granite and greisen.

Cassiterite usually occurs as veins or impregnations in granitic rocks, and is especially associated with the quartz-mica rock called greisen.

The wall rocks are usually strongly altered and in part are replaced by some of the above minerals, forming coarse-grained rocks which are called "greisen."

The latter is a pneumatolytic product consisting of quartz and tourmaline; it often contains white mica and thus passes by all stages into greisen.

They make it clear that there has been an introduction of fluorine and boron and a diminution in the alkalies during the transformation of the granitic rock into the greisen.