The principal accessory minerals, in addition to olivine and feldspar, are chromite and other spinels, garnet, magnetite, rutile, and scapolite.
en.wikipedia.org Feldspar crystals are seen at the margin of these massive formations.
en.wikipedia.org Clay minerals, for example can be formed by weathering of feldspar, which is the most common mineral present in igneous rock.
en.wikipedia.org Other incorporated silicate minerals may include, very minor amounts of plagioclase feldspar, mica in the form of muscovite and/or biotite, and amphibole (often hornblende).
en.wikipedia.org If a rock undergoes phyllic alteration, then orthoclase feldspar, biotite and various silicates are altered in addition to plagioclase.
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