Namesake Minerals #5

Over the next few weeks I’ll be covering minerals that are named after myths and legends. This week is dedicated to two minerals named after gods of the sea: aegirine and neptunite.


Aegirine with orthoclase 85 x 83mm in size, from Mount Malosa, Zomba District, Malawi (image by CarlesMillan from

Quick facts:

  • Silicate mineral
  • Commonly forms in alkali igneous rocks
  • Type locality: Rundemyr, Øvre Eiker, Buskerud, Norway
  • Formula: NaFe3+Si2O6
  • Crystal system: Monoclinic
  • Hardness: 6
  • Density: 3.5-3.6 g/cm3

As well as being found in alkali igneous rocks, aegirine also forms in carbonatites, pegmatites and metamorphic rocks from the blueschist facies. It can be found in slates as an authigenic mineral which means that it formed in place within the sediment; this is the opposite of a detrital mineral which formed somewhere else and was then transported to the sediment. Other common localities include Canada, America, Scotland and the Narsarsuk Pegmatite in Greenland.


Cluster of aegirine crystals, from near Malosa Mountain, Zomba District, Malawi (image by John Betts from

At first, aegirine didn’t have a name derived from a sea god. In 1821, P. H. Ström studied a specimen from Rundemyr in Norway and realised he had discovered a new mineral. He wanted to call it wernerin in honour of Abraham Gottlob Werner. However, it was named acmite by Jöns Jacob Berzelius who analysed the mineral. This name comes from the Greek word ‘αχμη’ which means spear point. In 1834, priest and mineralogist Hans Morten Thrane Esmark found a new mineral at Låven in Norway. Since it was found near to the sea, he named it aegirine after the Norse sea god Aegir.
Acmite and aegirine were originally thought to be two different minerals, an amphibole and a pyroxene respectively, but in 1871, Gustav Tschermak von Seysenegg proved that they were both pyroxene minerals. After this, acmite was regarded as a brown variety of green aegirine. In 1988, the decision was made to discredit acmite as a separate mineral species and make aegirine the official name. Analysis has shown that green aegirine specimens have more FeO, TiO2, MnO and CaO and a lower content of Fe2O3 than the brown varieties.


Aegir (image from

Aegirine is named after Aegir, the Norse god of the sea. He’s depicted as a giant with a crown of seaweed and he lives with his wife, Ran, and their nine daughters in a grand hall beneath the ocean. Aegir is known for hosting elaborate parties for the gods where he brews ale in a large cauldron.






Neptunite from Benitoite Gem Mine, San Benito County, California, USA (image by John Betts from

Quick facts:

  • Silicate mineral
  • Commonly associated with natrolite and benitoite
  • Type locality: Narsarsuk Pegmatite, Narsarsuk, Igaliko, Greenland
  • Formula: Na2KLiFe22+Ti2Si8O24
  • Crystal system: Monoclinic
  • Hardness: 5-6
  • Density: 3.19-3.23 g/cm3

Neptunite from San Benito Mountains, San Benito County, California, USA (image from

While neptunite was first discovered in a sample from the Narsarsuk Pegmatite in 1893, it’s main source is in San Benito County in California. In this locality, neptunite is found in natrolite veins which cut through glaucophane schist inclusions in a serpentinite body. It is also found in Russia, Canada and Australia. Neptunite appears black but if it is broken into thin pieces or held in front of a light source, its deep red colour can be seen. Neptunite is the iron-rich end member of a solid solution series with manganoneptunite, which is manganese-rich.



Neptunite and benitoite in a natrolite matrix, from Benitoite Gem Mine, San Benito County, California, USA (image by John Betts from

It’s common for mineral collectors to dissolve the natrolite matrix to reveal the stunning black crystals of neptunite. In the Benitoite Gem Mine, neptunite and benitoite are usually found together. Benitoite is a rare mineral and fluoresces under UV light.

neptune statue.jpg

Neptune statue on Virginia Beach, Virginia, USA (image by Erechtheus from

So, who is the god behind the mineral? Neptunite was given its name because it was found closely associated with aegirine at its type locality. Neptune (Neptunus in Latin) is the Roman god of the sea – he was initially a god of freshwater – and is the Roman version of the Greek god Poseidon. He is depicted as a bearded man with a trident and with fish or horses which draw his chariot. Neptune is the son of Opis (the goddess of earth) and Saturn (the god of agriculture among other things).









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