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Milanriederite

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About MilanriederiteHide

Formula:
(Ca18[REE])Fe3+Al4(Mg4Al4)(☐4)☐[Si2O7]4[(SiO4)10](OH)(OH)9
According to Mössbauer data, all iron in the mineral is trivalent.

The formula is a partial simplification of the full structural formula. The large (VII-IX)-coordinated (X4)2(X3)8(X2)8(X1) sites are here combined (e.g. Ca19) and are typically filled with Ca, although other large cations such as the REE may be present. The square-pyramidal Y1 site can host a variety of M2+ and M3+ ions and is the basis for the distinction of several species. The VI-coordinated Y2 site typically is filled with Al, whereas the also VI-coordinated Y3 site may contain Al, Mg, and other cations of similar charge and size. The tetrahedral T1 site is typically vacant but may contain B (less commonly Al); the trigonal T2 site is also typically vacant but may also contain B. Some of the (SiO4) may be replaced by (H4O4), akin to the Si4+ ↔︎ 4H+ hydrogarnet substitution. Among the oxygen that are not part of the silica tetrahedra, there are eight "O11" that typically occur as OH, two "O10" that are typically O & OH or OH & OH (the latter arrangement notably when Y1 is an M2+ cation). There may also be up to three "O12" that in most vesuvianite-group minerals are absent (and are not included here), but may be present particularly when T1 is occupied.

Note: The published formula by Chukanov et al., 2019 includes ∑(REE+Y) = 1.97 apfu (primarily in the X3 site), although this amount does not dominate the site and so might be disregarded when considering the end-member formula. However, the extra charge afforded by this REE inclusion appears necessary to provide charge balance for defining M2+>M3+ in the Y3 site, as full hydrogenation of the "O10" and "O11" positions would be otherwise insufficient. Indeed, the IMA formula includes more H than is permissible by the formula, and is also inconsistent with what Chukanov et al., 2019 report (9.96 apfu OH).

To address this inconsistency and to closer approximate the published analysis, one apfu of REE is included in the presented formula to maintain charge balance (although other charge-balancing mechanisms, such as the addition of B into the normally vacant T1 and/or T2 sites, may also be possible).
Colour:
dark brownish-red
Hardness:
6
Specific Gravity:
3.53
Crystal System:
Tetragonal
Name:
The mineral is named in honour of Czech mineralogist Professor Milan Rieder (b. 1940), in recognition to his contributions to mineralogy and his service to the international mineralogical community.
This page provides mineralogical data about Milanriederite.


Classification of MilanriederiteHide

Approved

Physical Properties of MilanriederiteHide

Colour:
dark brownish-red
Hardness:
Tenacity:
Brittle
Cleavage:
None Observed
Parting:
none
Fracture:
Irregular/Uneven
Density:
3.53(2) g/cm3 (Measured)    3.547 g/cm3 (Calculated)

Optical Data of MilanriederiteHide

Type:
Uniaxial (-)
RI values:
nω = 1.744(3) nε = 1.737(3)
Max Birefringence:
δ = 0.007
Image shows birefringence interference colour range (at 30µm thickness)
and does not take into account mineral colouration.
Surface Relief:
High

Chemical Properties of MilanriederiteHide

Formula:
(Ca18[REE])Fe3+Al4(Mg4Al4)(☐4)☐[Si2O7]4[(SiO4)10](OH)(OH)9

According to Mössbauer data, all iron in the mineral is trivalent.

The formula is a partial simplification of the full structural formula. The large (VII-IX)-coordinated (X4)2(X3)8(X2)8(X1) sites are here combined (e.g. Ca19) and are typically filled with Ca, although other large cations such as the REE may be present. The square-pyramidal Y1 site can host a variety of M2+ and M3+ ions and is the basis for the distinction of several species. The VI-coordinated Y2 site typically is filled with Al, whereas the also VI-coordinated Y3 site may contain Al, Mg, and other cations of similar charge and size. The tetrahedral T1 site is typically vacant but may contain B (less commonly Al); the trigonal T2 site is also typically vacant but may also contain B. Some of the (SiO4) may be replaced by (H4O4), akin to the Si4+ ↔︎ 4H+ hydrogarnet substitution. Among the oxygen that are not part of the silica tetrahedra, there are eight "O11" that typically occur as OH, two "O10" that are typically O & OH or OH & OH (the latter arrangement notably when Y1 is an M2+ cation). There may also be up to three "O12" that in most vesuvianite-group minerals are absent (and are not included here), but may be present particularly when T1 is occupied.

Note: The published formula by Chukanov et al., 2019 includes ∑(REE+Y) = 1.97 apfu (primarily in the X3 site), although this amount does not dominate the site and so might be disregarded when considering the end-member formula. However, the extra charge afforded by this REE inclusion appears necessary to provide charge balance for defining M2+>M3+ in the Y3 site, as full hydrogenation of the "O10" and "O11" positions would be otherwise insufficient. Indeed, the IMA formula includes more H than is permissible by the formula, and is also inconsistent with what Chukanov et al., 2019 report (9.96 apfu OH).

To address this inconsistency and to closer approximate the published analysis, one apfu of REE is included in the presented formula to maintain charge balance (although other charge-balancing mechanisms, such as the addition of B into the normally vacant T1 and/or T2 sites, may also be possible).
IMA Formula:
Ca19Fe3+Al4(Mg4Al4)Si18O67(OH)11

Crystallography of MilanriederiteHide

Crystal System:
Tetragonal
Class (H-M):
4/mmm (4/m 2/m 2/m) - Ditetragonal Dipyramidal
Space Group:
P4/nnc
Setting:
P4/nnc
Cell Parameters:
a = 15.6578(4) Å, c = 11.8597(5) Å
Ratio:
a:c = 1 : 0.757
Unit Cell V:
2,907.60 ų (Calculated from Unit Cell)
Z:
2

X-Ray Powder DiffractionHide

Powder Diffraction Data:
d-spacingIntensity
2.970Å(50)
2.774Å(100)
2.617Å(87)
2.481Å(30)
2.143Å(19)
1.676Å(17)
1.628Å(38)
1.570Å(12)

Type Occurrence of MilanriederiteHide

General Appearance of Type Material:
dipyramidal crystals up to 3 mm across.
Place of Conservation of Type Material:
Collections of the Fersman Mineralogical Museum, Russian Academy of Sciences, Leninskiy Prospekt 18-2, Moscow 119071, Russia, registration number 5224/1
Associated Minerals at Type Locality:
Reference:
Chukanov, N. V., Panikorovskii, T. L., Goncharov, A. G., Pekov, I. V., Belakovskiy, D. I., Britvin, S. N., ... & Vozchikova, S. A. (2019). Milanriederite,(Ca, REE) 19Fe3+ Al4 (Mg, Al, Fe3+) 8Si18O68 (OH, O) 10, a new vesuvianite-group mineral from the Kombat Mine, Namibia. European Journal of Mineralogy, 31(3), 637-646.

Synonyms of MilanriederiteHide

Relationship of Milanriederite to other SpeciesHide

Other Members of this group:
AlumovesuvianiteCa19AlAl4(Al6Mg2)(☐4)☐[Si2O7]4[(SiO4)10]O(OH)9Tet. 4/m : P4/n
CyprineCa19Cu2+Al4(Al6Mg2)(☐4)☐[Si2O7]4[(SiO4)10](OH)(OH)9Tet. 4/m : P4/n
FluorvesuvianiteCa19Fe3+Al4(Al6Mg2)(☐4)☐[Si2O7]4[(SiO4)10]O(F,OH)9Tet. 4/mmm (4/m 2/m 2/m)
HongheiteCa19Fe2+Al4(Fe3+,Mg)8(☐4)B[Si2O7]4[(SiO4)10]O(OH,O)9Tet. 4/mmm (4/m 2/m 2/m) : P4/nnc
MagnesiovesuvianiteCa19MgAl4(Al6Mg2)(☐4)☐[Si2O7]4[(SiO4)10](OH)(OH)9Tet. 4/m : P4/n
Manaevite-(Ce)(Ca13Ce4[H2O]2)Mg(Al3Mg)(Mg3Ti3Fe3+2)(☐4)☐[Si2O7]4[(SiO4)8(H4O4)2]O(OH)9Tet. 4/mmm (4/m 2/m 2/m) : P4/nnc
ManganvesuvianiteCa19Mn3+Al4(Al6Mg2)(☐4)☐[Si2O7]4[(SiO4)10]O(OH)9Tet. 4/m : P4/n
VesuvianiteCa19Fe3+Al4(Al6Mg2)(☐4)☐[Si2O7]4[(SiO4)10]O(OH)9Tet. 4/mmm (4/m 2/m 2/m) : P4/nnc
WiluiteCa19MgAl4(Al,Mg)8(B,☐)4☐[Si2O7]4[(SiO4)10]O(O,OH)9Tet. 4/mmm (4/m 2/m 2/m) : P4/nnc

Other InformationHide

Health Risks:
No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.

References for MilanriederiteHide

Reference List:
Sort by Year (asc) | by Year (desc) | by Author (A-Z) | by Author (Z-A)
Chukanov, N.V., Panikorovskii, T.L., Goncharov, A.G., Pekov, I.V., Belakovskiy,D.I., Britvin, S.N., Möckel, S., Vozchikova, S.A. (2018): Milanriederite, IMA 2018-041. CNMNC Newsletter No. 45, October 2018, page xxx; Mineralogical Magazine, 82, xxx-xxx; http://forum.amiminerals.it/viewtopic.php?f=5&t=14984 (retrieved 26.10.2018)
Chukanov, N. V., Panikorovskii, T. L., Goncharov, A. G., Pekov, I. V., Belakovskiy, D. I., Britvin, S. N., ... & Vozchikova, S. A. (2019). Milanriederite,(Ca, REE) 19Fe3+ Al4 (Mg, Al, Fe3+) 8Si18O68 (OH, O) 10, a new vesuvianite-group mineral from the Kombat Mine, Namibia. European Journal of Mineralogy, 31(3), 637-646.

Internet Links for MilanriederiteHide

Localities for MilanriederiteHide

This map shows a selection of localities that have latitude and longitude coordinates recorded. Click on the symbol to view information about a locality. The symbol next to localities in the list can be used to jump to that position on the map.

Locality ListHide

- This locality has map coordinates listed. - This locality has estimated coordinates. ⓘ - Click for further information on this occurrence. ? - Indicates mineral may be doubtful at this locality. - Good crystals or important locality for species. - World class for species or very significant. (TL) - Type Locality for a valid mineral species. (FRL) - First Recorded Locality for everything else (eg varieties). Struck out - Mineral was erroneously reported from this locality. Faded * - Never found at this locality but inferred to have existed at some point in the past (eg from pseudomorphs.)

All localities listed without proper references should be considered as questionable.
Namibia (TL)
 
  • Otjozondjupa Region
    • Grootfontein
      • Kombat
Chukanov, N.V., Panikorovskii, T.L., Goncharov, A.G., Pekov, I.V., Belakovskiy, D.I., Britvin, S.N., Möckel, S., Vozchikova, S.A. (2018): Milanriederite, IMA 2018-041. CNMNC Newsletter No. 45, October 2018, page xxx; Mineralogical Magazine, 82, xxx-xxx; http://forum.amiminerals.it/viewtopic.php?f=5&t=14984 (retrieved 26.10.2018)
 
Mineral and/or Locality  
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