Formula: NaFe3+Si2O

Species:  Silicates – (Inosilicates)

Name: First described as acmit by P. H. Ström (1821) from . Ström (1821) recognized it as a new mineral and suggested the name wernerin, after the german geologist, Abraham Gottlob Werner. But Berzelius (1821), who analyzed the mineral, named it achmit after the greek αχμη, spear point, due to the habit of the crystals.
Later, in 1834, the priest and mineralogist Hans Morten Thrane Esmark found a new mineral on Låven, Langesundsfjorden, Norway which was described and given the name aegirine, after Ægir (Aegir), the sea god in Norse mythology because the type location was along the sea shore (Berzelius 1835). Acmite and aegirine were first believed to be two separate species, one belonging to the amphiboles (acmite) and the other to the pyroxenes (aegirine). This was the case until 1871 when G. Tschermak showed that acmite and aegirine both belonged to the pyroxenes and are the same mineral. Acmite has been considered as a variety of aegirine (historically acmite had priority, so it should have been the other way around).

Co-Type Localities: Låven,Langesundsfjorden,Norway – Rundemyr, Øvre Eiker, Viken, Norway

Colour: Dark green to greenish black, reddish brown, black

Lustre: Vitreous

Hardness: 6

Density: 3.5 – 3.6

Crystal System: Monoclinic

Member of: Clinopyroxene Subgroup > Pyroxene Group