Aegirine

Aegirine is a sodium-iron pyroxene (NaFe³⁺Si₂O₆) belonging to the clinopyroxene group of inosilicates, prized by collectors for its dark, glassy, needle-like crystals. Typically green, brown, or greenish-black, aegirine forms slender prismatic crystals with lengthwise striations and sharp, spear-like terminations — a feature that earned its historical synonym acmite, from the Greek word for "point". It crystallizes in sodium-rich alkaline igneous rocks such as nepheline syenites, carbonatites, and pegmatites, and its formula was first defined at its Norwegian type locality.

The species was first described from Rundemyr and Låven in Norway, near Kongsberg, giving it its name after Ægir, the Norse sea god. Since then, exceptional aegirine has come from a handful of world-famous alkaline complexes: the classic black, freestanding prisms of Mont Saint-Hilaire in Quebec; the striking specimens on orthoclase and microcline from Mount Malosa in Malawi, which transformed collector interest in the species; and the acicular crystals intergrown with sodalite and feldspathoids from the Khibiny and Lovozero massifs on the Kola Peninsula. Other notable localities include Magnet Cove in Arkansas, the Ilímaussaq complex in Greenland, and Narsarsuk.

Aegirine typically occurs alongside other alkaline-suite minerals such as nepheline, arfvedsonite, eudialyte, astrophyllite, albite, and sodalite, making combination specimens especially desirable. Collectors seek aegirine for its sharp crystal habit, dramatic matrix contrast, and its role as a signature accessory mineral of the world's great peralkaline intrusions.