Lamprophyre
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Lamprophyres are uncommon, small-volume ultrapotassic igneous rocks primarily occurring as dikes, lopoliths, laccoliths, stocks, and small intrusions. They are alkaline silica-undersaturated mafic or
Minette (a type of lamprophyre), from Jáchymov in the Czech Republic
Microscope view (long dimension 2 mm) of a thin section of minette from the Colorado Plateau. Magnesium-rich biotite (P, phlogopite) and clinopyroxene (C) phenocrysts in a groundmass of alkali feldspar, pyroxene, and iron-titanium oxides.
A dike of minette near Shiprock, Navajo Volcanic Field
Ultramafic rock
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Ultramafic rocks are igneous and meta-igneous rocks with a very low silica content, generally >18% MgO, high FeO, low potassium, and are usually composed of greater than 90% mafic minerals. Earth's ma
Peridotite, a type of ultramafic rock
Melilitite from Hohenstoffeln (Hegau)