Analcime is a common constituent of all of the Oligocene rocks of the district, including phonolite, plagioclase phonolite, phonotephrite, tephriphonolite, vogesite, and monchiquite It occurs as drusy crystals in cavities, as irregular masses, as phenocrysts, and surrounding nepheline crystals (Lindgren and Ransome, 1906; Loughlin and Koschmann, 1935; Birmingham, 1987).
Kaersutite occurs as reddish-brown, 1 to 2-mm crystals in the groundmass of plagioclase phonolite, tephriphonolite, and, rarely, vogesite (Birmingham, 1987).
Orthoclase occurs with microcline in Proterozoic rocks of the district, as phenocrysts in plagioclase phonolite, as a major constituent of tephriphonolite and vogesite, as a part of the ground-mass in monchiquite and as transparent to translucent crystals ("adularia") in both the veins and the inner and outer parts of altered host rocks (replacing biotite and microcline) of vein and diatreme-hosted deposits.
Pargasite is very common as brown to olive-green microphenocrysts in vogesite, as tan megacrysts in monchiquite, and in tephriphonolite and plagioclase phonolite (Birmingham, 1987).
Phlogopite occurs as phenocrysts and as a constituent of the groundmass in vogesite and monchiquite (Birmingham, 1987; Thompson, 1992).
In vogesite its composition ranges from andesine to bytownite, and minor albite occurs in the groundmass of monchiquite (Lindgren and Ransome, 1906; Loughlin and Koschmann, 1935; Thompson, 1992).