Complex sentence: These rocks mainly consist of feldspar, quartz, mica, and amphibole minerals, which form interlocking, somewhat equigranular matrices of feldspar and quartz with scattered darker biotite mica and amphibole (often hornblende) peppering the lighter color minerals.
Split into simpler sentences: These rocks mainly consist of feldspar, quartz, mica, and amphibole minerals. These form interlocking somewhat equigranular matrix of feldspar and quartz with scattered darker biotite mica and amphibole (often hornblende) peppering the lighter color minerals.