Ishikawaite
A valid IMA mineral species - grandfathered
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About Ishikawaite
Formula:
U4+Fe2+Nb2O8
Colour:
Black
Lustre:
Sub-Adamantine, Vitreous, Sub-Vitreous, Resinous, Waxy
Hardness:
5 - 6
Specific Gravity:
6.2 - 6.4
Crystal System:
Monoclinic
Member of:
Name:
Described in 1922 by Yuji Shibata and Kenjiro Kimura for the type locality, being in the Ishikawa pegmatite district, more specifically Tomaki-Kannonyama (which, according to historical toponym tracing by Kota Harihara, is identical to today’s Kannonyama mine) and the Ōhashi river, both within the current Ishikawa town.
Ishikawaite was originally described in 1922 as being chemically similar to samarskite but richer in U and poorer in REEs. Decades later, Hanson et al. (1999) defined the species as the U-analogue of samarskite, giving it a formula of (U,Fe)NbO4, in which (U,Th)⁴⁺ is dominant at the A-site of the outdated ABO₄ formula. Following the redefinition of samarskite-(Y) by Britvin et al. (2019) as AMB₂O₈ and the proposition of columbite supergroup by Chukanov et al. (2023), its structural relation to samarskite has been questioned as insufficiently studied, and its current status in the IMA list is Q (questionable species).
(The mineral is metamict; published data on XRD pattern and cell parameters are for heated material, with no guarantee that the structure restored was the original one.)
Ishikawaite is sometimes coated by brown to red-brown or yellow surface alterations. May be partially or completely metamict.
(The mineral is metamict; published data on XRD pattern and cell parameters are for heated material, with no guarantee that the structure restored was the original one.)
Ishikawaite is sometimes coated by brown to red-brown or yellow surface alterations. May be partially or completely metamict.
Unique Identifiers
Mindat ID:
2050
Long-form identifier:
mindat:1:1:2050:9
IMA Classification of Ishikawaite
Approved, 'Grandfathered' (first described prior to 1959)
IMA Formula:
(U4+,Fe2+,Y)Nb5+O4
First published:
1922
Classification of Ishikawaite
4.DB.25
4 : OXIDES (Hydroxides, V[5,6] vanadates, arsenites, antimonites, bismuthites, sulfites, selenites, tellurites, iodates)
D : Metal: Oxygen = 1:2 and similar
B : With medium-sized cations; chains of edge-sharing octahedra
4 : OXIDES (Hydroxides, V[5,6] vanadates, arsenites, antimonites, bismuthites, sulfites, selenites, tellurites, iodates)
D : Metal: Oxygen = 1:2 and similar
B : With medium-sized cations; chains of edge-sharing octahedra
8.1.4.1
8 : MULTIPLE OXIDES CONTAINING NIOBIUM,TANTALUM OR TITANIUM
1 : ABO4
8 : MULTIPLE OXIDES CONTAINING NIOBIUM,TANTALUM OR TITANIUM
1 : ABO4
18.4.4
18 : Niobates and Tantalates
4 : Niobates and tantalates containing both U and rare earths
18 : Niobates and Tantalates
4 : Niobates and tantalates containing both U and rare earths
Mineral Symbols
As of 2021 there are now IMA–CNMNC approved mineral symbols (abbreviations) for each mineral species, useful for tables and diagrams.
| Symbol | Source | Reference for Standard |
|---|---|---|
| Ikw | IMA–CNMNC | Warr, L.N. (2021). IMA–CNMNC approved mineral symbols. Mineralogical Magazine, 85(3), 291-320. doi:10.1180/mgm.2021.43 |
Physical Properties of Ishikawaite
Sub-Adamantine, Vitreous, Sub-Vitreous, Resinous, Waxy
Transparency:
Translucent, Opaque
Comment:
Broken surfaces are generally vitreous to sub-adamantine. Thin splinters may show smoky brown translucency.
Colour:
Black
Streak:
Dark brown; black
Hardness:
5 - 6 on Mohs scale
Hardness Data:
Measured
Cleavage:
None Observed
Fracture:
Conchoidal
Density:
6.2 - 6.4 g/cm3 (Measured)
Chemistry of Ishikawaite
Mindat Formula:
U4+Fe2+Nb2O8
Element Weights:
Elements listed:
Common Impurities:
Ca,Ce,Ta,Ti,Sn,Si,Th,Mn,Mg,REE
Crystallography of Ishikawaite
Crystal System:
Monoclinic
Cell Parameters:
a = 5.562 Å, b = 9.934 Å, c = 5.243 Å
β = 93.9°
β = 93.9°
Ratio:
a:b:c = 0.56 : 1 : 0.528
Unit Cell V:
289.02 ų (Calculated from Unit Cell)
Morphology:
Black rod-like to somewhat bladed crystals {100}. Anhedral masses.
Forms include c{001}, a{100}, s{210}, h{320}, m{110}, n{140}, b{010}, r{144}, and d{101}.
Forms include c{001}, a{100}, s{210}, h{320}, m{110}, n{140}, b{010}, r{144}, and d{101}.
Comment:
usually metamict
X-Ray Powder Diffraction
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 2.972 Å | (100) |
| 3.103 Å | (98) |
| 3.73 Å | (38) |
| 2.615 Å | (30) |
| 2.476 Å | (28) |
| 2.819 Å | (26) |
| 3.60 Å | (22) |
Comments:
Metamict. Published data given for heated material; no guarantee that the original structure was restored!
Geological Environment
Paragenetic Mode(s):
| Paragenetic Mode | Earliest Age (Ga) |
|---|---|
| Stage 4b: Highly evolved igneous rocks | >3.0 |
| 34 : Complex granite pegmatites |
Geological Setting:
Granite pegmatite
Type Occurrence of Ishikawaite
General Appearance of Type Material:
Prismatic orthorhombic-appearing black crystals.
Place of Conservation of Type Material:
No designated type material.
Geological Setting of Type Material:
NYF-pegmatite.
Associated Minerals at Type Locality:
Other Language Names for Ishikawaite
Relationship of Ishikawaite to other Species
Member of:
Other Members of Samarskite Group:
| Calciosamarskite | (Ca,U4+)Fe3+(Nb,Ta,Ti)2O8 | Orth. mmm(2/m2/m2/m) |
| Samarskite-(Y) | YFe3+Nb2O8 | Mon. 2/m : P2/b |
| Samarskite-(Yb) | YbFe3+(Nb,Ta)2O8 | Mon. 2/m : P2/b |
| Shakhdaraite-(Y) | ScYNb2O8 | Mon. 2/m : P2/b |
| Yttrotantalite-(Y) | (Y,U,Fe2+)(Ta,Nb)(O,OH)4 | Orth. |
Chemically related to group(s):
| Samarskite Group | A3+B3+C5+2O8 |
Common Associates
Associations Based on Photo Data:
| 11 photos of Ishikawaite associated with Columbite-(Fe) | Fe2+Nb2O6 |
| 7 photos of Ishikawaite associated with Quartz | SiO2 |
| 6 photos of Ishikawaite associated with Microcline | K(AlSi3O8) |
| 2 photos of Ishikawaite associated with Annite | KFe2+3(AlSi3O10)(OH)2 |
| 2 photos of Ishikawaite associated with Albite | Na(AlSi3O8) |
| 2 photos of Ishikawaite associated with Corundum | Al2O3 |
| 1 photo of Ishikawaite associated with Muscovite | KAl2(AlSi3O10)(OH)2 |
| 1 photo of Ishikawaite associated with Nontronite | Na0.3Fe2((Si,Al)4O10)(OH)2 · nH2O |
| 1 photo of Ishikawaite associated with Biotite | K(Fe2+/Mg)2(Al/Fe3+/Mg/Ti)([Si/Al/Fe]2Si2O10)(OH/F)2 |
| 1 photo of Ishikawaite associated with 'Oligoclase' | (Na,Ca)[Al(Si,Al)Si2O8] |
Related Minerals - Strunz-mindat Grouping
| 4.DB. | Tianhongqiite | CrTiO3(OH) |
| 4.DB. | Nioboheftetjernite | ScNbO4 |
| 4.DB. | Huangshanite | Fe3+TaO4 |
| 4.DB. | Nioboixiolite-(Mn2+) | (Nb0.67Mn2+0.33)O2 |
| 4.DB. | Shakhdaraite-(Y) | ScYNb2O8 |
| 4.DB.05 | Varlamoffite | Sn1-xFexO2-x(OH) |
| 4.DB.05 | Argutite | GeO2 |
| 4.DB.05 | Cassiterite | SnO2 |
| 4.DB.05 | Rutile | TiO2 |
| 4.DB.05 | Plattnerite | PbO2 |
| 4.DB.05 | Tripuhyite | Fe3+Sb5+O4 |
| 4.DB.05 | Tugarinovite | MoO2 |
| 4.DB.05 | Pyrolusite | Mn4+O2 |
| 4.DB.10 | Byströmite | MgSb2O6 |
| 4.DB.10 | Ordoñezite | ZnSb2O6 |
| 4.DB.10 | Tredouxite | NiSb2O6 |
| 4.DB.10 | Tapiolite-(Mn) | Mn2+Ta2O6 |
| 4.DB.10 | Tapiolite-(Fe) | Fe2+Ta2O6 |
| 4.DB.15a | Paramontroseite | V4+O2 |
| 4.DB.15a | Ramsdellite | Mn4+O2 |
| 4.DB.15b | Akhtenskite | ε-Mn4+O2 |
| 4.DB.15c | Nsutite | (Mn4+,Mn2+)(O,OH)2 |
| 4.DB.20 | Scrutinyite | α-PbO2 |
| 4.DB.20 | Nioboixiolite-([]) | (Nb0.8◻0.2)4+O2 |
| 4.DB.25 | Yttrocolumbite-(Y) | Y(U4+,Fe2+)Nb2O8 |
| 4.DB.25 | Calciosamarskite | (Ca,U4+)Fe3+(Nb,Ta,Ti)2O8 |
| 4.DB.25 | Samarskite-(Yb) | YbFe3+(Nb,Ta)2O8 |
| 4.DB.25 | Ixiolite-(Sc) | (Ta0.5Sc0.5)O2 |
| 4.DB.25 | Ixiolite-(Fe2+) | (Ta0.67Fe2+0.33)O2 |
| 4.DB.25 | Ixiolite-(Mn2+) | (Ta0.67Mn2+0.33)O2 |
| 4.DB.25 | Nioboixiolite-(Fe2+) | (Nb0.67Fe2+0.33)O2 |
| 4.DB.25 | Srilankite | TiO2 |
| 4.DB.25 | Samarskite-(Y) | YFe3+Nb2O8 |
| 4.DB.25 | Nioboixiolite-(Fe3+) | (Nb0.5Fe3+0.5)O2 |
| 4.DB.30 va | Wolframite Group | |
| 4.DB.30 | Rossovskyite | (Fe3+,Ta)(Nb,Ti)O4 |
| 4.DB.30 | Huanzalaite | MgWO4 |
| 4.DB.30 | Heftetjernite | ScTaO4 |
| 4.DB.30 | Hübnerite | MnWO4 |
| 4.DB.30 | Sanmartinite | (Zn,Fe)WO4 |
| 4.DB.30 | Ferberite | FeWO4 |
| 4.DB.30 | 'Krasnoselskite' | CoWO4 |
| 4.DB.35 | Qitianlingite | (Fe,Mn)2(Nb,Ta)2WO10 |
| 4.DB.35 | Tantalaeschynite-(Ce) | Ce(TiTa)O6 |
| 4.DB.35 | Tantalite-(Mg) | (Mg,Fe2+)(Ta,Nb)2O6 |
| 4.DB.35 | Columbite-(Mn) | Mn2+Nb2O6 |
| 4.DB.35 | Tantalite-(Mn) | Mn2+Ta2O6 |
| 4.DB.35 | Columbite-(Fe) | Fe2+Nb2O6 |
| 4.DB.35 | Columbite-(Mg) | (Mg,Fe,Mn)(Nb,Ta)2O6 |
| 4.DB.35 | Tantalite-(Fe) | Fe2+Ta2O6 |
| 4.DB.40 | Ferrotitanowodginite | Fe2+TiTa2O8 |
| 4.DB.40 | 'Wolframowodginite' | Mn(Mn,Sn,Fe,Ta)(W,Ta,Nb)2O8 |
| 4.DB.40 | Lithiotantite | LiTa3O8 |
| 4.DB.40 | Lithiowodginite | LiTa3O8 |
| 4.DB.40 | Titanowodginite | Mn2+TiTa2O8 |
| 4.DB.40 | Tantalowodginite | (Mn2+0.5◻0.5)TaTa2O8 |
| 4.DB.40 | Wodginite | Mn2+Sn4+Ta2O8 |
| 4.DB.40 | Ferrowodginite | Fe2+Sn4+Ta2O8 |
| 4.DB.45 | Tivanite | V3+TiO3(OH) |
| 4.DB.50 | Carmichaelite | (Ti,Cr,Fe)[O2-x(OH)x] |
| 4.DB.55 | Alumotantite | AlTaO4 |
| 4.DB.60 | Biehlite | ((Sb,As)O)2[MoO4] |
Radioactivity
Radioactivity:
| Element | % Content | Activity (Bq/kg) | Radiation Type |
|---|---|---|---|
| Uranium (U) | 39.1700% | 9,792,500 | α, β, γ |
| Thorium (Th) | 0.0000% | 0 | α, β, γ |
| Potassium (K) | 0.0000% | 0 | 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: –
| Distance | Dose rate | Risk |
|---|---|---|
| 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
Fluorescence of Ishikawaite
Not fluorescent in UV.
Other Information
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 Ishikawaite
mindat.org URL:
https://www.mindat.org/min-2050.html
Please feel free to link to this page.
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References for Ishikawaite
Localities for Ishikawaite
Showing 41 localities.
symbol to view information about a locality.
The Locality List
- 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).
All localities listed without proper references should be considered as questionable.
Afghanistan | |
| Hanson et al. (1999) | |
Australia | |
| Brugger et al. (2011) |
Bulgaria | |
| Tarassov et al. (2022) |
| Georgieva et al. (2023) |
Canada | |
| Dixon et al. (2014) |
China | |
| Zhang Peishan et al. (1996) |
| Rubo Zhang and Fengming Han (1983) |
| www.smartminerals.com (2004) | |
Czech Republic | |
| Škoda et al. (2004) |
Egypt | |
| Yehia H. Dawood (2011) +1 other reference |
| Abdel Gawad et al. (2022) |
| Kamar et al. (2022, August) |
France | |
| MONCHOUX P. et al. (2006) |
Japan | |
| Min Mag 63 (1999) |
| Kimura (1922) |
| Alfredo Petrov collection (ex- Bill Pinch collection) | |
| Petrov (n.d.) | |
| Kimura (1922) | |
Poland | |
| PIECZKA et al. 2010: Nb-Ta minerals in ... |
| Pieczka et al. (2012) +1 other reference | |
Romania | |
| HÎRTOPANU et al. (2014) |
Russia | |
| Yu.S. Kobyashev data |
| Pavel M. Kartashov (n.d.) | |
| www.mindat.org (n.d.) | |
| webmineral.ru (2021) |
| Alekseev (2025) |
| Alekseev (2025) | |
| Alekseev et al. (2018) |
| Zakharov et al. (2022) |
| Ivanova et al. (2020) |
USA | |
| Simmons et al. (2006) |
| Hanson et al. (2003) |
| Hanson et al. (2003) +1 other reference |
| King et al. (1994) +1 other reference |
| Thompson et al. (1998) | |
| King et al. (1994) +1 other reference |
| Hanson et al. (1998) | |
| King et al. (1994) +1 other reference | |
| King et al. (1994) | |
| King et al. (1994) +1 other reference | |
| Rocks & Min. 80:246 (2005) |
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Ishikawa town, Ishikawa District, Fukushima Prefecture, Japan