Lomonosovite


Lomonosovite is a phosphate–silicate mineral with the idealized formula Na10Ti422O4 early Na5Ti2O2 or Na2Ti2Si2O9*Na3PO4.
The main admixtures are niobium, manganese and iron.

Discovery and name

The mineral was discovered by V.I. Gerasimovskii in Lovozersky agpaitic massif. Named for Mikhail Lomonosov - famous Russian poet, chemist and philosopher, but the earlier - mining engineer.

Crystal structure

According to X-ray data, lomonosovite structure was determined is triclinic unit cell with parameters: a = 5.44 Å, b = 7.163 Å, c = 14.83 Å, α = 99°, β = 106°, and γ = 90°, usually centrosymmetric , but acentric varieties are also reported.
The crystal structure of lomonosovite is based on three-layer HOH packets consisting of a central octahedral O layer and two outer heteropolyhedral H layers. Ti- and Na centered octahedra are distinguished in the O layer, whereas the H layers are composed of Ti-centered octahedra and Si2O7 diorthogroups,. The interpacket space includes Na+ cations and PO43- anions.

Properties

Lomonosovite forms lamellar and tabular crystals with perfect cleavage. It is macroscopically brown, from cinnamon-brown to black. It is transparent in thin plates. The luster vitreous to adamantine.
Its pleochroism is strong from colorless to brown. The refractive index is = 1.654-1.670 = 1.736 - 1.750 =1.764-1.778 2V=56-69.
Hardness 3-4 Density 3.12 - 3.15.

Origin

Accessory mineral of peralkaline agpaitic nepheline syenites important mineral of agpaitic pegmatites and peralkaline fenites.