Orthite and melilite (blue) with quartz, from a thin section in crossed polarized light.
General
Category
Sorosilicates
Formula (repeating unit)
(Ca,Na)2(Al,Mg,Fe2+)[(Al,Si)SiO7]
Strunz classification
9.BB.**
Crystal system
Tetragonal
Space group
P421m (no. 113)
Identification
Color
Yellowish, greenish brown
Crystal habit
Massive – granular
Cleavage
Distinct on {001}, weak on {110}
Fracture
Uneven
Mohs scale hardness
5–5.5
Luster
Vitreous – greasy
Streak
white
Diaphaneity
Translucent
Specific gravity
2.9–3.0
Optical properties
Uniaxial (−)
Refractive index
nω = 1.632 – 1.669 nε = 1.626 – 1.658
Birefringence
δ = 0.006 – 0.011
References
[1][2]
A view down onto the sheets of the A2B(T2O7) 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.
Melilite refers to a mineral of the melilite group. Minerals of the group are solid solutions of several endmembers, the most important of which are gehlenite and åkermanite. A generalized formula for common melilite is (Ca,Na)2(Al,Mg,Fe2+)[(Al,Si)SiO7]. Discovered in 1793 near Rome, it has a yellowish, greenish-brown color. The name derives from the Greek words meli (μέλι) "honey" and lithos (λίθους) "stone".The name refers to a group of minerals (melilite group) with chemically similar composition, nearly always minerals in åkermanite-gehlenite series.[3]
Minerals of the melilite group are sorosilicates. They have the same basic structure, of general formula A2B(T2O7). The melilite structure consist of pairs of fused TO4, where T may be Si, Al, B, in bow-tie form. Sharing one corner, the formula of the pair is T2O7. These bow-ties are linked together into sheets by the B cations. The sheets are held together by the A cations, most commonly calcium and sodium. Aluminium may sit on either the T or the B site.
Minerals with the melilite structure may show a cleavage parallel to the (001) crystallographic directions and may show weaker cleavage perpendicular to this, in the {110} directions. Melilite is tetragonal.
The important endmembers of common melilite are åkermanite Ca2Mg(Si2O7) and gehlenite Ca2Al[AlSiO7]. Many melilites also contain appreciable iron and sodium.
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]. Some structures formed by replacing one oxygen by F or OH: leucophanite (Ca,Na)2(Be,Al)[Si2O6(F,OH)], jeffreyite (Ca,Na)2(Be,Al)[Si2O6(O,OH)], and meliphanite (Ca,Na)2(Be,Al)[Si2O6(OH,F)].
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 refers to a mineral of the melilite group. Minerals of the group are solid solutions of several endmembers, the most important of which are gehlenite...
(marble). Associated minerals include nepheline, leucite, titanian andradite, melilite, augite, sanidine, biotite, phlogopite and apatite. The type locality is...
igneous rocks, include some light-colored ferromagnesian minerals, such as melilite, in the mafic mineral fraction. Accessory minerals, such as zircon or apatite...
volcano known for its semipermanent lava lake activity, erupts lava made of melilite nephelinite. The unusual chemical makeup of this igneous rock may be a...
Gehlenite, (Ca2Al[AlSiO7]), is a sorosilicate, Al-rich endmember of the melilite complete solid solution series with akermanite. The type locality is in...
locality it occurs with wollastonite, spurrite, perovskite, merwinite, melilite and gehlenite. It occurs in contact metamorphosed limestones and chalks...
containing, in various proportions mainly the minerals nepheline, leucite, melilite, kalsilite, and clinopyroxene. This very low silica composition results...
December 2020. Mindat Simon, S. B. and L. Grossman, A comparative study of melilite and fassaite in Types B1 and B2 refractory inclusions, Geochimica et Cosmochimica...
phenocrysts of mica and/or amphibole together with lesser clinopyroxene and/or melilite set in a groundmass which may consist (either singly or in various combinations)...
tephrite, phonotephrite, clinopyroxene, amphibole, magnetite, olivine, melilite and leucite. The main magma chamber is about 16–24 km deep, into the ocean...
diamond-bearing rocks (kimberlite, lamproite and lamprophyre) lack certain minerals (melilite and kalsilite) that are incompatible with diamond formation. In kimberlite...
larnite-normative nephelinites and basanites along with lesser olivine melilite nephelinites, phonolites and tholeiitic and alkali basalts. List of fault...
Classification and Nomenclature of Volcanic Rocks, Lamprophyres, Carbonatites and Melilite Rocks. Recommendations and Suggestions. Neues Jahrbuch für Mineralogie...
phases of ferrous slag contain calcium-rich olivine-group silicates and melilite-group silicates. Slag from steel mills in ferrous smelting is designed...
nephelinic, leucitic and analcitic series evolves from nephelinite or melilite through analcite to leucitite or wyomingite. The latter two may also be...
which make their appearance with some frequency are melanite, garnet and melilite. The plutonic leucite-bearing rocks are leucite syenite and missourite...
Classification and Nomenclature of Volcanic Rocks, Lamprophyres, Carbonatites and Melilite Rocks. Recommendations and Suggestions. Neues Jahrbuch für Mineralogie...
jennite, portlandite and jasmundite. In an Austrian occurrence near Kloch, melilite, mayenite, wollastonite, kalsilite and corundum are found. Within the Hatrurim...
pyrrhotite, grossular, spinel, afwillite, jennite, portlandite, jasmundite, melilite, kalsilite and corundum in the limestone xenoliths. In the Hatrurim it...
precludes a rock from being classified as a lamproite: primary plagioclase, melilite, monticellite, kalsilite, nepheline, Na-rich alkali feldspar, sodalite...
Gugiaite is a melilite mineral, named for the Chinese village of Gugia where it was first discovered. Its chemical formula is Ca2BeSi2O7. It occurs mostly...
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