Aegirine is a common mineral, a member of the Pyroxene group (a group of rock forming minerals found in many igneous and metamorphic rocks). It is known for its long slender crystals, often referred to as “spears” and “arrows”. It is commonly colored green to dark-green, and less commonly black, reddish-black and brown. It is commonly opaque, but can be translucent, and in rare occasions, transparent. It is very collectable, and well crystallized specimens are sought after by collectors. It often occurs in association in Microline, Albite, Natrolite, Quartz and Rhodochrosite to name a few.

The crystal system for Aegirine is monoclinc, typically forming as long, slender prismatic or bladed crystals, often embedded in matrix and in radiating masses and interlocking thin prismatic crystals. Other forms include fibrous, sprays of acicular crystals and occasionally doubly terminated. Crystals are commonly striated.

Notable localities include Brazil, Canada, Greenland, Malawi, Norway, Russia, and USA (Arkansas).