melilite

{{Infobox mineral | name = Melilite | category = Sorosilicates | boxwidth = | boxbgcolor = | image = Melilite (GeoDIL number - 1968).jpg | imagesize = | caption = Melilite – each of the pieces is about 1 cm across | strunz = 9.BB.** | formula = {{chem2|(Ca,Na)2(Al,Mg,Fe^{2+})[(Al,Si)SiO7]}} | molweight = | color = Yellowish, greenish brown | habit = Massive – granular | system = Tetragonal | symmetry = P21m (no. 113) | twinning = | cleavage = Distinct on {001}, weak on {110} | fracture = Uneven | tenacity = | mohs = 5–5.5 | luster = Vitreous – greasy | streak = white | diaphaneity = Translucent | gravity = 2.9–3.0 | density = | polish = | opticalprop = Uniaxial (−) | refractive = nω = 1.632 – 1.669 nε = 1.626 – 1.658 | birefringence = δ = 0.006 – 0.011 | pleochroism = | 2V = | dispersion = | extinction = | length fast/slow = | fluorescence= | absorption = | melt = | fusibility = | diagnostic = | solubility = | other = | alteration = | references = }} thumb|300px|right|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.

thumb|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.