Momoiit

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Momoiit
General and classification
other names

Yamatoit, IMA 2009-026

chemical formula Mn 2+ 3 V 3+ 2 Si 3 O 12
Mineral class
(and possibly department) 		Silicates and Germanates
System no. to Strunz
and to Dana 		9.AD.25 ( 8th edition : 8 / A.08-138)
51.4.4.5
Similar minerals Uvarowit , goldmanite
Crystallographic Data
Crystal system cubic
Crystal class ; symbol cubic hexakisoctahedral; 4 / m  3  2 / m
Space group Ia 3 d (No. 230)Template: room group / 230
Lattice parameters a  = 11.9242 (natural mixed crystal)  Å
Formula units Z  = 8
Physical Properties
Mohs hardness Please complete!
Density (g / cm 3 ) natural mixed crystal: 4.01 (calculated)
Cleavage not observed
colour greenish yellow to emerald green
Line color pale green
transparency Please complete!
shine Glass gloss
Crystal optics
Refractive index n  = 1.86 (natural mixed crystal)
Birefringence isotropic, e.g. T. slightly birefringent

The mineral momoiite is a very rare island silicate from the garnet group and has the idealized chemical composition Mn 2+ 3 V 3+ 2 Si 3 O 12 . It crystallizes in the cubic crystal system with the structure of garnet.

Depending on the vanadium and manganese content, momoiite forms greenish-yellow to emerald-green crystal aggregates , which are rarely larger than 1–2 mm. The individual crystals have a diameter of 0.1-0.2 mm and have a glass luster .

Momoiite-rich garnets are formed during the contact metamorphosis of vanadium-containing manganese deposits. The type locality is a skarn in the Kurase Mine near the city of Saijō in Ehime Prefecture on Shikoku Island in Japan .

Etymology and history

The first manganese and vanadium-rich garnets were described by Hitoshi Momoi in 1964 in a manganese-rich skarn from the Yamato mine. Contrary to the practice of the International Mineralogical Association (IMA), he introduced the name Yamatoite for the hypothetical manganese-vanadiun end link with the composition Mn 2+ 3 V 3+ 2 Si 3 O 12 , although none of his analyzes exceeded 50 mol% this composition. Yamatoite has therefore not been an IMA recognized name for a mineral or a variety. Nevertheless, it was listed in the mineral systematics for a long time.

It was only 46 years later that Hidekazu Tanaka's working group was able to detect manganese-accentuated vanadium garnet in a renewed examination of the grenade of several Japanese manganese deposits. They discarded the name introduced by the late professor Hitoshi Momoi (1930-2002) and named the new garnet after him, who was the first to recognize the manganese-vanadium end link.

So far, no occurrences of momoiit outside of Japan have been described.

classification

The structural classification of the International Mineralogical Association (IMA) is one of the Momoiit to Garnet supergroup, where he along with almandine , Andradite , Calderit , Eringait , Goldmanit , Grossular , Knorringit , Morimotoit , majorite , Menzerit- (Y) , pyrope , Rubinit , Spessartine and Uvarowite form the garnet group with 12 positive charges on the tetrahedrally coordinated lattice position.

The obsolete, but still used the eighth edition of the mineral classification by Strunz still leads Yamatoit instead Momoiit along with almandine, Andradite, Calderit, Goldmanit, Grossular, Henritermierit , Hibschite , Holtstamit , Hydrougrandit , katoite , Knorringit, Morimotoit, majorite, pyrope, Schorlomit , Spessartin, Uvarowit and Wadalit in the "garnet group" with the system no. VIII / A.08 within the department of " Island Silicates (Nesosilicates)".

The 9th edition of Strunz's mineral systematics, which has been in effect since 2001, also counts the momoiit to the “garnet group” with the system no. 9.AD.25 within the department of "Island Silicates (Nesosilicates)". However, this is further subdivided according to the possible presence of further anions and the coordination of the cations involved , so that the mineral is classified according to its composition in the subsection “Island silicates without additional anions; Cations in octahedral [6] and usually greater coordination ”can be found.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , also classifies the momoiit under the name Yamatoit in the section of "island silicate minerals ". Here it is together with andradite, goldmanite, grossular, uwarovite in the "garnet group (Ugrandite series)" with the system no. 51.04.03b to be found in the subsection “ Island silicates: SiO 4 groups only with cations in [6] and> [6] coordination ”.

Chemism

Momoiite with the idealized composition [X] Mn 2+ 3 [Y] V 3+ [Z] Si 3 O 12 is the vanadium analog of Spessartine ( [X] Mn 2+ 3 [Y] Al [Z] Si 3 O 12 ) or the manganese analog of goldmanite ( [X] Ca 3 [Y] V 3+ [Z] Si 3 O 12 ) with which it forms mixed crystals according to the exchange reactions

  • [X] Mn 2+ = [X] Ca 2+ , (Spessartine)
  • [Y] V 3+ = [Y] Al 3+ (goldmanite).

The following composition is given for the momoiit from the type locality:

  • [X] (Mn 1.80 Ca 1.12 Mg 0.04 ) [Y] (V 3+ 1.51 Al 0.52 ) [Z] Si 3.00 O 12 ,

where [X], [Y] and [Z] indicate the positions in the garnet structure.

Crystal structure

Momoiite crystallizes with cubic symmetry in the space group Ia 3 d (space group no. 230) with 8 formula units per unit cell . The natural mixed crystal from the type locality has the lattice parameter a  = 11.9242  Å . Template: room group / 230

The structure is that of garnet . Manganese (Mn 2+ ) occupies the dodecahedral X positions surrounded by 8 oxygen ions, vanadium (V 3+ ) the octahedral Y position surrounded by 6 oxygen ions and the tetrahedral Z position surrounded by 4 oxygen ions is exclusively silicon (Si 4+ ) occupied.

The sometimes slight birefringence of the crystals indicates a lower symmetry, as in Grossular or Goldmanit.

Education and Locations

So far (2018) there are only four documented locations of Momoiit, all in Japan. In all of these deposits, momoiite formed at low pressure during the contact metamorphosis of manganese, vanadium and calcium-containing pelites .

In the type locality , the Kurase Mine near the city of Saijō in the prefecture of Ehime on the island of Shikoku in Japan , momoiite occurs in Skarn together with rhodochrosite , tephroit , rhodonite and vuorelainenite . Depending on the local composition of the parent rock, garnets rich in momoiite, rich in Spessartine or rich in goldmanite were formed.

Another deposit is the Hokkejino Mine in Kyoto Prefecture on the island of Honshu , Japan. Here, momoiite is also found in a metamorphic manganese deposit, where it occurs together with rhodonite, tephroit, celsian , rhodochrosite and pyrophanite .

The third deposit investigated by Tanaka and his co-workers is a medium-grade contact metamorphic, stratified manganese deposit that is mined in the Fujii Mine in Fukui Prefecture, also on the main island of Honshu. Here, garnet rich in momoiite is associated either with quartz, rhodonite, molybdenite , rhodochrosite and manganese-rich vanadoallanite (La) or, in quartz-free areas, with rhodonite, tephroite, rhodochrosite and mineral .

In the same year (2010) another working group described momoiite-rich grenades from heaps of the Matsumaezawa ore body of the Tanohata Mine in Iwate Prefecture on the main island of Honshu, Japan. Several very rare manganese minerals have been described in this contact-metamorphic manganese deposit, which was changed by a granodiorite intrusion. Momoiit occurs here in quartz-rich pegmatitartigen courses along with Rhodonit, Serandit and vanadium-containing Aegirin , titanite , Allanit , potassic ferric Leakeit and Suzukiit , Watatsumiit , Yoshimurait , potassium feldspar , Hyalophane , Pyrophanit and strontium-containing fluorapatite on.

See also

Web links

Individual evidence

  1. ^ A b c Michael Fleischer: New Mineral Names: Yamatoite . In: The American Mineralogist . tape 50 , 1965, pp. 810 ( minsocam.org [PDF; 711 kB ; accessed on February 25, 2018]).
  2. ↑ a b c d e f g h i j k l m n H. Tanaka, S. Endo, T. Minakawa, M.Enami, D. Nishio-Hamane, H. Miura and A. Hagiwara: Momoiite, (Mn2 +, Ca) 3 (V3 +, Al) 2Si3O12, a new manganese vanadium garnet from Japan . In: Journal of Mineralogical and Petrological Sciences . tape 105 , 2010, p. 92–96 ( jst.go.jp [PDF; 729 kB ; accessed on February 25, 2018]).
  3. ↑ a b c Satoshi Matsubara, Ritsuro Miyawaki, Kazumi Yokoyama, Masako Shigeoka, Hiroshi Miyajima, Yasumitsu Suzuki, Osamu Murakami and Takashi Ishibashi: Momoiite and nagashimalite from the Tanohata mine, Iwate Prefecture, Japan . In: Bull. Natl. Mus. Nat. Sci., Ser. C . tape 36 , 2010, p. 1–6 ( kahaku.go.jp [PDF; 3.2 MB ; accessed on February 25, 2018]).
  4. ↑ a b List of localities for Momoiit in the Mineralienatlas and Mindat
  5. ^ Edward S. Grew, Andrew J. Locock, Stuart J. Mills, Irina O. Galuskina, Evgeny V. Galuskin and Ulf Hålenius: IMA Report - Nomenclature of the garnet supergroup . In: American Mineralogist . tape 98 , 2013, p. 785–811 ( main.jp [PDF; 2,3 MB ; accessed on July 8, 2017]).