ABSTRACT
A Geological Medley altered facet. Everyone has seen grains of mica glittering in pavements. Mica is inextinguishable, with no more radiance than quartz. We see the mica constantly in sandstones and granites. Felspar is opaque. So the light that passes through the mica and the quartz on the surface of granite is reflected straight back by the opaque felspar. In sandstones, the cement between and behind the grains often has this role. Once more, the comparative luminosity of so many limestones is due to the closeness of their grains. This luminosity, let me repeat, is not to be confused with transparency. Alabaster has a far more pronounced inner light; but alabaster, to a greater extent than marble, is transparent: so, the identification between an opaque or bluff appearance and a slight roseate glow is less marked in alabastrine and many semi-precious stones whose clean-cut qualities are those of gems rather than of building and sculptural blocks.
