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Lomonosovite

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Phosphate–silicate mineral
Lomonosovite
General
CategoryMineral
Formula
(repeating unit)		Na10Ti4(Si2O7)2(PO4)2O4
IMA symbolLom
Crystal systemTriclinic
Unit cella = 5.49 Å, b = 7.11 Å, c = 14.5 Å α = 101°, β = 96°, γ = 90°
Identification
CleavagePerfect
FractureIrregular
TenacityBrittle
Mohs scale hardness3–4
Density3.12 – 3.15
Optical propertiesBiaxial(−)
Refractive indexnα = 1.670 nβ = 1.750 nγ = 1.778
Birefringence0.108
2V angle56°
A image of a rock with Lomonisovite and bornemanite
Image of Lomonisovite(beige) and bornemanite(white)

Lomonosovite is a phosphate–silicate mineral with the idealized formula Na10Ti4(Si2O7)2(PO4)2O4 early Na5Ti2(Si2O7)(PO4)O2 or Na2Ti2Si2O9*Na3PO4.

The main admixtures are niobium (up to 11.8% Nb2O5), manganese (up to 4.5 %MnO) and iron (up to 2.8%).

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 (sp. gr. P-1), but acentric varieties (polytype) 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, (like in other heterophyllosilicates, for example lamprophyllite). The interpacket space includes Na cations and PO4 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 α {\displaystyle \alpha } = 1.654–1.670 β {\displaystyle \beta } = 1.736 – 1.750 γ {\displaystyle \gamma } =1.764–1.778 2V=56–69.

Hardness 3–4 Density 3.12 – 3.15.

Origin

Accessory mineral of peralkaline agpaitic nepheline syenites (like Khibina and Lovozero massif, Russia, Ilimaussaq intrusion, Greenland) important mineral of agpaitic pegmatites and peralkaline fenites.

References

  1. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. "COMMISSION ON NEW MINERALS".
  3. ^ "Handbook of mineralogy" (PDF).
  4. ^ Rastsvetaeva, Zaitsev, Pekov (2020). "Crystal Structure of Niobium-Rich Lomonosovite with Symmetry P1 from the Khibiny Massif (Kola Peninsula)". Crystallography Reports. 65 (3): 22–427. Bibcode:2020CryRp..65..422R. doi:10.1134/S1063774520030268. S2CID 219784165.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  5. Gerasimovskii, V. I. "Lomonosovite, a new mineral". Dokl. Akad. Nauk SSSR. 70.
  6. "Maburg. Song of Yu.Lores".
  7. ^ Rastsvetaeva, Simonov, Belov (1971). "Crystalline structure of lomonosovite, Na5Ti2O2". Dokl. Akad. Nauk SSSR. 197 (1): 81–84.{{cite journal}}: CS1 maint: multiple names: authors list (link)


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