Felsite

noun

1. A fine-grained, light-colored igneous rock, composed chiefly of feldspar and quartz.
2. A compact, very hard rock, almost flinty in texture. made up of quartz and orthoclase feldspar intimately mixed.
3. A finegrained rock, flintlike in fracture, consisting essentially of orthoclase feldspar with occasional grains of quartz.
4. A fine grained <xref>volcanic</xref> <xref>extrusive</xref> rock, generally light in color, composed of <xref>felsic</xref> <xref>minerals</xref>.
5. Any light-colored <xref>volcanic</xref> rock whose true <xref>mineralogy</xref> is not yet determined.