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lamprophyre A dark-coloured, strongly porphyritic, intrusive igneous rock, containing abundant euhedral phenocrysts of biotite and/or amphibole which can be accompanied by phenocrysts of olivine, diopside, apatite, or opaque oxides, set in a mafic, felsic, or glassy groundmass. There are no felsic phenocrysts present in this rock type. The lamprophyres are subdivided into a number of types on the basis of their most abundant mafic component and the presence and type of feldspar in the groundmass. Lamprophyre types include minette, kerstantite, alnöite, vogesite, camptonite, and monchiquite, and are found intruded as dykes and sills.