Chemistry:Lomonosovite
| Lomonosovite | |
|---|---|
| General | |
| Category | Mineral |
| Formula (repeating unit) | Na10Ti4(Si2O7)2(PO4)2O4 |
| Crystal system | Triclinic |
| Unit cell | a = 5.49 Å, b = 7.11 Å, c = 14.5 Å α = 101°, β = 96°, γ = 90° |
| Identification | |
| Cleavage | Perfect |
| Fracture | Irregular |
| Tenacity | Brittle |
| Mohs scale hardness | 3–4 |
| Density | 3.12 – 3.15 |
| Optical properties | Biaxial(−) |
| Refractive index | nα = 1.670 nβ = 1.750 nγ = 1.778 |
| Birefringence | 0.108 |
| 2V angle | 56° |
Lomonosovite is a phosphate–silicate mineral with the idealized formula Na10Ti4(Si2O7)2(PO4)2O4 [2] early Na5Ti2(Si2O7)(PO4)O2 or Na2Ti2Si2O9*Na3PO4.[3]
The main admixtures are niobium (up to 11.8% Nb2O5), manganese (up to 4.5 %MnO) and iron (up to 2.8%).[4]
Discovery and name
The mineral was discovered by V.I. Gerasimovskii [5] in Lovozersky agpaitic massif. Named for Mikhail Lomonosov – famous Russian poet, chemist and philosopher, but the earlier – mining engineer.[6]
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),[7] but acentric varieties (polytype) are also reported.[4]
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 PO43- anions.[7]
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 [math]\displaystyle{ \alpha }[/math]= 1.654–1.670 [math]\displaystyle{ \beta }[/math] = 1.736 – 1.750 [math]\displaystyle{ \gamma }[/math]=1.764–1.778 2V=56–69.[3]
Hardness 3–4 Density 3.12 – 3.15.[3]
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.[3]
References
- ↑ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine 85 (3): 291–320. doi:10.1180/mgm.2021.43. Bibcode: 2021MinM...85..291W. https://www.cambridge.org/core/journals/mineralogical-magazine/article/imacnmnc-approved-mineral-symbols/62311F45ED37831D78603C6E6B25EE0A.
- ↑ "COMMISSION ON NEW MINERALS". http://cnmnc.main.jp/imalist.htm.
- ↑ 3.0 3.1 3.2 3.3 "Handbook of mineralogy". http://www.handbookofmineralogy.org/pdfs/lomonosovite.pdf.
- ↑ 4.0 4.1 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. doi:10.1134/S1063774520030268. Bibcode: 2020CryRp..65..422R. https://www.researchgate.net/publication/341480954.
- ↑ Gerasimovskii, V. I.. "Lomonosovite, a new mineral". Dokl. Akad. Nauk SSSR 70.
- ↑ "Maburg. Song of Yu.Lores". http://www.bard.ru.com/php/clip_clip.php?id=370.15.
- ↑ 7.0 7.1 Rastsvetaeva, Simonov, Belov (1971). "Crystalline structure of lomonosovite, Na5Ti2[Si2O7][PO4]O2". Dokl. Akad. Nauk SSSR 197 (1): 81–84.
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