Melilite

Some other compositions with the melilite structure include: alumoåkermanite (Ca,Na)2(Al,Mg,Fe2+)(Si2O7), okayamalite Ca2B[BSiO7], gugiaite Ca2Be[Si2O7], hardystonite Ca2Zn[Si2O7], barylite BaBe2[Si2O7], andremeyerite BaFe2+2[Si2O7].

New members of this mineral group were artificially grown and became intensively studied due to their multiferroic property, i.e., they simultaneously show ferroelectric and magnetic ordering at low temperatures.

This gives rise to peculiar optical properties, for example Ba2Co(Ge2O7) shows giant directional dichroism (different absorption for counter-propagating light beams)[4] and hosts magnetically switchable chirality.

[4] Melilite with compositions dominated by the endmembers akermanite and gehlenite is widely distributed but uncommon.

[5] Isotope ratios of magnesium and some other elements in these inclusions are of great importance in deducing processes that formed the Solar System.

Melilitite is a volcanic rock composed of over 90% melilite, with small amounts of olivine, clinopyroxene, and perovskite.

However, more modern classification schemes avoid the term katungite and describe the rock instead as (for example) kalsilite-leucite-olivine melilitite, depending on the most abundant accessory minerals.

A view down onto the sheets of the A 2 B ( T 2 O 7 ) melilite structure. The A sites are yellow spheres, the B sites are pale orange tetrahedra, and the T sites are blue tetrahedra. Oxygen atoms (not shown) are on the corners of the tetrahedra.
Crossed polarized light image of melilite in Moiliili lava flow, Moiliili Quarry, Honolulu, O‘ahu, Hawai‘i surrounded by matrix of granular nepheline and volcanic glass. This rock (nepheline-melilite basalt) was erupted during rejuvenated volcanism on O‘ahu.