Vote for your favorite mineral in #MinCup26! - Azurite vs. Smithsonite
It's carbonate-vs-carbonate to kick off Mineral Cup 2026 with copper-rich Azurite against zinc-rich Smithsonite.
Log InRegister
Quick Links : The Mindat ManualThe Rock H. Currier Digital LibraryMindat Newsletter [Free Download]
Home PageAbout MindatThe Mindat ManualHistory of MindatCopyright StatusWho We AreContact UsAdvertise on Mindat
Donate to MindatCorporate SponsorshipSponsor a PageSponsored PagesMindat AdvertisersAdvertise on Mindat
Learning CenterWhat is a mineral?The most common minerals on earthInformation for EducatorsMindat ArticlesThe ElementsThe Rock H. Currier Digital LibraryGeologic TimeExplore Fossils
Minerals by PropertiesMinerals by ChemistryMineral Visual ExplorerAdvanced Locality SearchRandom MineralRandom LocalitySearch by minIDLocalities Near MeSearch ArticlesSearch GlossaryMore Search Options
Search For:
Mineral Name:
Locality Name:
Keyword(s):
 
The Mindat ManualAdd a New PhotoRate PhotosLocality Edit ReportCoordinate Completion ReportAdd Glossary Item
Mining CompaniesStatisticsUsersMineral MuseumsClubs & OrganizationsMineral Shows & EventsThe Mindat DirectoryDevice SettingsThe Mineral QuizTime Machine
Photo SearchPhoto GalleriesSearch by ColorPhoto Colour ExplorerNew Photos TodayNew Photos YesterdayMembers' Photo GalleriesPast Photo of the Day GalleryPhotography

Fenaksite

A valid IMA mineral species
This page is currently not sponsored. Click here to sponsor this page.
09005910017657569819945.jpg
Fenaksite

Rasvumchorr Mt, Murmansk Oblast, Russia
03305350017657569829312.jpg
Fenaksite

Rasvumchorr Mt, Murmansk Oblast, Russia
08228940017271923073294.jpg
Fenaksite, etc.

Rasvumchorr Mt, Murmansk Oblast, Russia
09877180017593978006935.jpg
Fenaksite

Rasvumchorr Mt, Murmansk Oblast, Russia
01250390017271923066384.jpg
Fenaksite

Rasvumchorr Mt, Murmansk Oblast, Russia
08228940017271923073294.jpg
Fenaksite, etc.

Rasvumchorr Mt, Murmansk Oblast, Russia
09005910017657569819945.jpg
Fenaksite

Rasvumchorr Mt, Murmansk Oblast, Russia
06442400017271923112891.jpg
Fenaksite

Rasvumchorr Mt, Murmansk Oblast, Russia
Hide all sections | Show all sections

About FenaksiteHide

Formula:
(K,Na)4(Fe,Mn)2(Si4O10)2(OH,F)
Colour:
Light rose
Lustre:
Pearly
Hardness:
5 - 5½
Specific Gravity:
2.744
Crystal System:
Triclinic
Name:
Named for its chemical composition (Fe, Na, K, Si).
The iron analogue of manaksite.


Unique IdentifiersHide

Mindat ID:
1475
Long-form identifier:
mindat:1:1:1475:1

IMA Classification of FenaksiteHide

Classification of FenaksiteHide

Strunz-mindat (2026):
9.DG.70

9 : SILICATES (Germanates)
D : Inosilicates
G : Inosilicates with 3-periodic single and multiple chains
Dana 8th ed.:
70.1.1.2

70 : INOSILICATES Column or Tube Structures
1 : Column or Tube Structures with columnar silicate units
Hey's CIM Ref.:
14.20.8

14 : Silicates not Containing Aluminum
20 : Silicates of Fe and alkali metals

Mineral SymbolsHide

As of 2021 there are now IMA–CNMNC approved mineral symbols (abbreviations) for each mineral species, useful for tables and diagrams.

SymbolSourceReference for Standard
FnkIMA–CNMNCWarr, L.N. (2021). IMA–CNMNC approved mineral symbols. Mineralogical Magazine, 85(3), 291-320. doi:10.1180/mgm.2021.43

Physical Properties of FenaksiteHide

Lustre:
Pearly
Transparency:
Transparent, Translucent
Comment:
On cleavages
Colour:
Light rose
Hardness:
5 - 5½ on Mohs scale
Cleavage:
Distinct/Good
Two, intersecting at an angle of 122 degrees.
Density:
2.744 g/cm3 (Measured)    2.74 g/cm3 (Calculated)

Optical Data of FenaksiteHide

Type:
Biaxial (+)
RI values:
nα = 1.541 nβ = 1.560 nγ = 1.567
2V:
Measured: 84° , Calculated: 60°
Max. Birefringence:
δ = 0.026
Based on recorded range of RI values above.

Interference Colours:
The colours simulate birefringence patterns seen in thin section under crossed polars. They do not take into account mineral colouration or opacity.

Michel-Levy Bar The default colours simulate the birefringence range for a 30 µm thin-section thickness. Adjust the slider to simulate a different thickness.

Grain Simulation You can rotate the grain simulation to show how this range might look as you rotated a sample under crossed polars. Each grain retains its interference colour (retardation) while its brightness falls to black at extinction and reaches a maximum between extinction positions.

Surface Relief:
Moderate
Dispersion:
weak

Chemistry of FenaksiteHide

Mindat Formula:
(K,Na)4(Fe,Mn)2(Si4O10)2(OH,F)
Element Weights:
Element% weight
O40.492 %
Si27.078 %
K18.848 %
Fe13.461 %
H0.122 %

Calculated from ideal end-member formula.
Elements listed:
F, Fe, H, K, Mn, Na, O, Si - search for minerals with similar chemistry
Common Impurities:
Ti,Al,Mg

Crystallography of FenaksiteHide

Crystal System:
Triclinic
Class (H-M):
1 - Pinacoidal
Space Group:
P1
Cell Parameters:
a = 8.24 Å, b = 9.97 Å, c = 6.97 Å
α = 98.58°, β = 114.47°, γ = 105.02°
Ratio:
a:b:c = 0.826 : 1 : 0.699
Unit Cell V:
481.46 ų (Calculated from Unit Cell)
Z:
2

Crystal StructureHide

Load
Unit Cell | Unit Cell Packed
2x2x2 | 3x3x3 | 4x4x4
Show
Big Balls | Small Balls | Just Balls | Spacefill
Polyhedra Off | Si Polyhedra | All Polyhedra
Remove metal-metal sticks
Display Options
Black Background | White Background
Perspective On | Perspective Off
2D | Stereo | Red-Blue | Red-Cyan
View
CIF File    Best | x | y | z | a | b | c
Rotation
Stop | Start
Labels
Console Off | On | Grey | Yellow
IDSpeciesReferenceLinkYearLocalityPressure (GPa)Temp (K)
0019813FenaksiteBrandao P, Rocha J, Reis M S, dos Santos A M, Jin R (2009) Magnetic properties of KNaMSi4O10 compounds (M=Mn,Fe,Cu) Journal of Solid State Chemistry 182 253-2582009synthetic0293
0012511FenaksiteRozhdestvenskaya I V, Bannova I I, Nikishova L V, Soboleva T V (2004) The crystal structure of fenaksite K2Na2Fe2Si8O20 Doklady Earth Sciences 398 1029-10332004synthetic0293
0015598FenaksiteGolovachev V P, Drozdov Y N, Kuz'min E A, Belov N V (1971) The crystal structure of phenaxite FeNaK(Si4O10)(KNaFe[Si4O10]) Soviet Physics Doklady 15 902-9041971Khibiny massif, Kola Peninsula, Russia0293
CIF Raw Data - click here to close

X-Ray Powder DiffractionHide

Powder Diffraction Data:
d-spacingIntensity
3.03 Å(100)
3.55 Å(70)
3.44 Å(70)
2.46 Å(70)
2.88 Å(60)
2.71 Å(60)
1.875 Å(60)

Geological EnvironmentHide

Paragenetic Mode(s):
Paragenetic ModeEarliest Age (Ga)
Stage 4b: Highly evolved igneous rocks>3.0
35 : Ultra-alkali and agpaitic igneous rocks

Type Occurrence of FenaksiteHide

Type Locality:
ⓘ Material'naya Adit, Yukspor Mountain, Murmansk Oblast, Russia
General Appearance of Type Material:
Grains up to 2-4 cm in diameter.
Place of Conservation of Type Material:
Geology Museum, Kola Branch, Academy of Sciences, Apatity, 1780; Vernadsky Geological Museum, Moscow, 46626; A.E. Fersman Mineralogical Museum, Academy of Sciences, Moscow, Russia, 61123, 61124, 62013.
Associated Minerals at Type Locality:
Aegirine-augiteAlbiteDelhayeliteEudialyteNepheline
Reference:
Dorfman, M.D., Rogachev, D.D., Goroshchenko, Z.I., Mokretsova, A.V. (1959) Fenaksite - a new mineral. Trudy Mineralogicheskogo Muzeya Akademiya Nauk SSSR, 9, 152-157.

Synonyms of FenaksiteHide

Other Language Names for FenaksiteHide

Relationship of Fenaksite to other SpeciesHide

Member of:
Litidionite Group
Other Members of Litidionite Group:
CalcinaksiteKNaCa(Si4O10) · H2OTric. 1 : P1
EnricofrancoiteKNaCaSi4O10Tric. 1 : P1
LitidioniteKNaCuSi4O10Tric. 1 : P1
ManaksiteKNaMnSi4O10Tric. 1 : P1

Common AssociatesHide

Associations Based on Photo Data:
3 photos of Fenaksite associated with Delhayelite(Na,K)10Ca5Al6Si32O80(Cl2,F2,SO4)3 · 18H2O
1 photo of Fenaksite associated with AenigmatiteNa4[Fe2+10Ti2]O4[Si12O36]
1 photo of Fenaksite associated with AegirineNaFe3+Si2O6
1 photo of Fenaksite associated with Lamprophyllite(Na,Mn2+)3(Sr,Na)2(Ti,Fe3+)3(Si2O7)2O2(OH,O,F)2

Related Minerals - Strunz-mindat GroupingHide

9.DG.Barrydawsonite-(Y)Na1.5Y0.5CaSi3O8(OH)Mon. 2/m : P21/b
9.DG.ParatobermoriteCa5AlSi5O16(OH) · 5H2OMon. 2/m
9.DG.CalcinaksiteKNaCa(Si4O10) · H2OTric. 1 : P1
9.DG.AlvesiteNaKZrSi6O15 · 2H2OOrth. mmm(2/m2/m2/m)
9.DG.02SteedeiteNaMn2[Si3BO9](OH)2Tric. 1 : P1
9.DG.02NolzeiteNaMn2[Si3BO9](OH)2 · 2H2OTric. 1 : P1
9.DG.05MurakamiiteLiCa2Si3O8(OH)Tric. 1 : P1
9.DG.05SeranditeNaMn2+2Si3O8(OH)Tric. 1 : P1
9.DG.05BustamiteCaMn2+(Si2O6)Tric. 1 : P1
9.DG.05PectoliteNaCa2Si3O8(OH)Tric. 1 : P1
9.DG.05TanohataiteLiMn2Si3O8(OH)Tric. 1 : P1
9.DG.05DalnegorskiteCa5Mn2+(Si3O9)2Tric. 1 : P1
9.DG.05'Wollastonite-1A'CaSiO3Tric. 1 : P1
9.DG.05WollastoniteCa3(Si3O9)Tric. 1 : P1
9.DG.05FerrobustamiteCaFe2+(Si2O6)Tric. 1
9.DG.05SchizoliteNaCaMnSi3O8(OH)Tric. 1 : P1
9.DG.07CascanditeCaScSi3O8(OH)Tric. 1
9.DG.08PlombièriteCa5Si6O16(OH)2 · 7H2OOrth.
9.DG.10ClinotobermoriteCa5Si6O17 · 5H2OMon.
9.DG.10RiversideiteCa5Si6O16(OH)2 · 2H2O Orth.
9.DG.10TobermoriteCa5Si6O17 · 5H2OMon. 2 : P21
9.DG.12JusiteNa2Ca15Al4Si16O54 · 17H2O
9.DG.12KenotobermoriteCa4Si6O15(OH)2 · 5H2OMon.
9.DG.15FoshagiteCa4(Si3O9)(OH)2Tric. 1 : P1
9.DG.20JenniteCa9(Si3O9)2(OH)8 · 8H2OTric. 1 : P1
9.DG.20KameneviteK2TiSi3O9 · H2OOrth. 222 : P212121
9.DG.25ParaumbiteK3Zr2H(Si3O9)2 · nH2OOrth. mm2
9.DG.25UmbiteK2(Zr,Ti)Si3O9 · H2OOrth. 222 : P212121
9.DG.30SørenseniteNa4SnBe2Si6O16(OH)4Mon. 2/m : B2/b
9.DG.32Escheite Ca2NaMnTi5[Si12O34]O2(OH)3 · 12H2OOrth. mm2 : Ama2
9.DG.35XonotliteCa6(Si6O17)(OH)2Mon. 2/m : B2/m
9.DG.40HillebranditeCa2(SiO3)(OH)2Orth. mmm(2/m2/m2/m) : Cmcm
9.DG.45ZoriteNa8(Ti,Nb)5(Si6O17)2(OH,O)5 · 14H2OOrth.
9.DG.45ChivruaiiteCa4(Ti,Nb)5(Si6O17)2(OH,O)5 · 13-14H2OOrth. mmm(2/m2/m2/m) : Cmmm
9.DG.50Haineaultite(Na,Ca)5Ca(Ti,Nb)5(Si6O17)2(OH,F)8 · 5H2OOrth. 222 : C222
9.DG.55EpididymiteNa2Be2Si6O15 · H2OOrth. mmm(2/m2/m2/m) : Pnma
9.DG.60EudidymiteNa2Be2Si6O15 · H2OMon. 2/m : B2/b
9.DG.65ElpiditeNa2ZrSi6O15 · 3H2OOrth.
9.DG.65PatyniteNaKCa4[Si9O23]Tric. 1 : P1
9.DG.67WhelaniteCu2+2Ca6[Si6O17(OH)](CO3)(OH)3 · 2H2OOrth. mm2 : Pnn2
9.DG.70EnricofrancoiteKNaCaSi4O10Tric. 1 : P1
9.DG.70YusupoviteNa2Zr(Si6O15) · 2.5H2OMon. 2/m : B2/m
9.DG.70LitidioniteKNaCuSi4O10Tric. 1 : P1
9.DG.70ManaksiteKNaMnSi4O10Tric. 1 : P1
9.DG.75SenkevichiteCsKNaCa2TiO[Si7O18](OH)Tric. 1 : P1
9.DG.75TinaksiteK2Na(Ca,Mn2+)2TiO[Si7O18(OH)]Tric.
9.DG.75TokkoiteK2Ca4[Si7O18(OH)](OH,F)Tric.
9.DG.80FluorcanasiteK3Na3Ca5Si12O30F4 · H2OMon. m : Bm
9.DG.80CanasiteK3Na3Ca5Si12O30(OH)4Mon. m : Bm
9.DG.85MiseriteK1.5-x(Ca,Y,REE)5(Si6O15)(Si2O7)(OH,F)2 · yH2OTric.
9.DG.90FrankameniteK3Na3Ca5(Si12O30)(F,OH)4 · H2OTric. 1 : P1
9.DG.92Charoite(K,Sr)15-16(Ca,Na)32[Si6O11(O,OH)6]2[Si12O18(O,OH)12]2[Si17O25(O,OH)18]2(OH,F)4 · ~3H2OMon. 2/m : P21/m
9.DG.95YuksporiteK4(Ca,Na)14(Sr,Ba)2(◻,Mn,Fe)(Ti,Nb)4(O,OH)4(Si6O17)2(Si2O7)3(H2O,OH)3Mon. 2/m : P21/m
9.DG.97Eveslogite(Na,K,Ca,Sr,Ba)48 [(Ti,Nb,Mn,Fe2+)12Si48O144(OH)12](F,OH,Cl)14Mon. 2/m : P2/m

RadioactivityHide

Radioactivity:
Element % Content Activity (Bq/kg) Radiation Type
Uranium (U) 0.0000% 0 α, β, γ
Thorium (Th) 0.0000% 0 α, β, γ
Potassium (K) 18.8479% 5,843 β, γ

For comparison:

  • Banana: ~15 Bq per fruit
  • Granite: 1,000–3,000 Bq/kg
  • EU exemption limit: 10,000 Bq/kg

Note: Risk is shown relative to daily recommended maximum exposure to non-background radiation of 1000 µSv/year. Note that natural background radiation averages around 2400 µSv/year so in reality these risks are probably extremely overstated! With infrequent handling and safe storage natural radioactive minerals do not usually pose much risk.

Interactive Simulator:

Note: The mass selector refers to the mass of radioactive mineral present, not the full specimen, also be aware that the matrix may also be radioactive, possibly more radioactive than this mineral!

Activity: –

DistanceDose rateRisk
1 cm
10 cm
1 m

The external dose rate (D) from a radioactive mineral is estimated by summing the gamma radiation contributions from its Uranium, Thorium, and Potassium content, disregarding daughter-product which may have a significant effect in some cases (eg 'pitchblende'). This involves multiplying the activity (A, in Bq) of each element by its specific gamma ray constant (Γ), which accounts for its unique gamma emissions. The total unshielded dose at 1 cm is then scaled by the square of the distance (r, in cm) and multiplied by a shielding factor (μshield). This calculation provides a 'worst-case' or 'maximum risk' estimate because it assumes the sample is a point source and entirely neglects any self-shielding where radiation is absorbed within the mineral itself, meaning actual doses will typically be lower. The resulting dose rate (D) is expressed in microsieverts per hour (μSv/h).

D = ((AU × ΓU) + (ATh × ΓTh) + (AK × ΓK)) / r2 × μshield

Other InformationHide

Notes:
Decomposed by acids with the deposition of silica.
Fuses easily before the blowpipe to a green glass; in a reducing flame, the powder becomes magnetic.
Health Risks:
No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.

Internet Links for FenaksiteHide

References for FenaksiteHide

Localities for FenaksiteHide

Showing 9 localities.

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.
Hide all sections | Show all sections

Locality ListHide

- This locality has map coordinates listed. - This locality has estimated coordinates. ⓘ - Click for references and 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 (e.g. from pseudomorphs).

All localities listed without proper references should be considered as questionable.
Russia
 
  • Murmansk Oblast
    • Koashva Mt
Arzamastsev et al. (2008)
Bertil Otter
Pekov (1998)
[World of Stones 95:5-6
Arzamastsev et al. (2008) +1 other reference
O Dziallas collection +1 other reference
      • Rasvumchorr Mine
Sokolova et al. (2005) +1 other reference
Pekov (1998)
    • Yukspor Mountain
Dorfman et al. (1959) +2 other references
Quick NavTopAbout FenaksiteUnique IdentifiersIMA Classification Classification Mineral SymbolsPhysical Properties Optical Data Chemistry Crystallography Crystal StructureX-Ray Powder DiffractionGeological EnvironmentType Occurrence SynonymsOther LanguagesRelationshipsCommon AssociatesStrunz-MindatRadioactivityOther InformationInternet Links References Localities Locality List
 
and/or  
Mindat.org® is an outreach project of the Hudson Institute of Mineralogy, a 501(c)(3) not-for-profit organization. Mindat® and mindat.org® are registered trademarks of the Hudson Institute of Mineralogy.
Copyright © mindat.org and the Hudson Institute of Mineralogy 1993-2026, except where stated. Most political location boundaries are © OpenStreetMap contributors. Mindat.org relies on the contributions of thousands of members and supporters. Founded in 2000 by Jolyon Ralph and Ida Chau.
Content on this site may not be used to train, fine-tune, or otherwise develop artificial intelligence or machine learning models without prior written permission - see our Terms & Conditions.
To cite: Ralph, J., Von Bargen, D., Martynov, P., Zhang, J., Que, X., Prabhu, A., Morrison, S. M., Li, W., Chen, W., & Ma, X. (2025). Mindat.org: The open access mineralogy database to accelerate data-intensive geoscience research. American Mineralogist, 110(6), 833–844. doi:10.2138/am-2024-9486.
Privacy Policy - Terms & Conditions - Contact Us / DMCA issues - Report a bug/vulnerability Current server date and time: September 1, 2026 14:52:38 Page updated: August 19, 2026 01:35:43
Go to top of page