Murmanite

(from Murmansk Oblast, where the mineral is widespread), a rare mineral of the silicate class, structurally belonging to the phyllosilicates. The crystallochemical formula is Na₂MnTi₃[Si₂O₇]₂ (OH)₄.H₂O. Usually the composition includes up to 10 percent Nb₂O₅, up to 2 percent ZrO₂, and up to 8 percent P₂O₅. The P₂O₅, probably in the form of sodium phosphate, is not bonded crystallochemically with the silicate structure of the principal mineral.

Murmanite crystallizes in the triclinic system, forming flakes that range in size from microscopic to 2.5. cm across. In pegmatites, these flakes can be as large as 10 cm in diameter. The mineral has a hardness on Mohs’ scale of 2.5–4; its density is 2,400–3,100 kg/m³. The color is lilac-pink or bright pink; altered varieties can be yellow-brown or dark brown. Murmanite is nontransparent. Its luster on the cleavage planes is vitreous or pearly; in fracture, the luster is greasy. The mineral is found only in alkaline rocks of the nepheline syenite family and pegmatites of this family.