Tuhualite
A valid IMA mineral species - grandfathered
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About Tuhualite
Formula:
NaFe2+Fe3+Si6O15
Na may be replaced by minor K.
Colour:
Dark blue to black, violet
Hardness:
3 - 4
Specific Gravity:
2.89
Crystal System:
Orthorhombic
Member of:
Name:
From the Maori "Tuhua" (obsidian), the original name for Mayor Island, New Zealand.
Type Locality:
Unique Identifiers
Mindat ID:
4045
Long-form identifier:
mindat:1:1:4045:3
IMA Classification of Tuhualite
Approved, 'Grandfathered' (first described prior to 1959)
First published:
1932
Classification of Tuhualite
9.DN.05
9 : SILICATES (Germanates)
D : Inosilicates
N : Inosilicates with 6-periodic double chains
9 : SILICATES (Germanates)
D : Inosilicates
N : Inosilicates with 6-periodic double chains
66.3.4.1
66 : INOSILICATES Double-Width,Unbranched Chains,(W=2)
3 : Amphiboles - Ca-Na subgroup
66 : INOSILICATES Double-Width,Unbranched Chains,(W=2)
3 : Amphiboles - Ca-Na subgroup
16.18.3
16 : Silicates Containing Aluminum and other Metals
18 : Aluminosilicates of Fe and alkalis
16 : Silicates Containing Aluminum and other Metals
18 : Aluminosilicates of Fe and alkalis
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 |
|---|---|---|
| Tuh | 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 Tuhualite
Transparency:
Translucent
Colour:
Dark blue to black, violet
Hardness:
3 - 4 on Mohs scale
Tenacity:
Very brittle
Cleavage:
Distinct/Good
Three good on (001), (010), (100).
Three good on (001), (010), (100).
Density:
2.89(2) g/cm3 (Measured) 2.86 g/cm3 (Calculated)
Optical Data of Tuhualite
Type:
Biaxial (+)
RI values:
nα = 1.608(1) nβ = 1.612 nγ = 1.621(3)
2V:
Measured: 70° to 91°, Calculated: 68°
Max. Birefringence:
δ = 0.013
Based on recorded range of RI values above.
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.
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:
High (positive)
Relative to Canada balsam mounting medium (n ≈ 1.537).
Relative to Canada balsam mounting medium (n ≈ 1.537).
This shows the grain boundary and Becke line effect under plane-polarised
light, based on the contrast between this mineral's average refractive
index and the mounting medium. It does not take into account mineral
colouration.
In focus
Interference Figure:
This shows the idealized biaxial acute bisectrix (Bxa) interference figure
- the conoscopic view for a grain cut perpendicular to the acute bisectrix, using
this mineral's 2V. The two small white dots mark the melatopes - the points
where the two optic axes emerge - and are shown only when they fall within the
field of view. The coloured bands are isochromatics, and the dark bands are
isogyres.
Rotate the stage: at 0°/90° the isogyres form a cross through the melatopes; at 45° they pull apart into curved hyperbolas. That splitting on rotation - absent in a uniaxial figure - is the standard diagnostic test for telling biaxial minerals from uniaxial ones. If 2V is large, the melatopes may fall outside the field of view, as they often do at the microscope too.
Rotate the stage: at 0°/90° the isogyres form a cross through the melatopes; at 45° they pull apart into curved hyperbolas. That splitting on rotation - absent in a uniaxial figure - is the standard diagnostic test for telling biaxial minerals from uniaxial ones. If 2V is large, the melatopes may fall outside the field of view, as they often do at the microscope too.
Dispersion:
Strong, r < v.
Optical Extinction:
X = a; Y = b; Z = c.
Pleochroism:
Strong
Comments:
X = colourless to pale lavender; Y = violet, lavender, Z = intense purplish-blue.
Comments:
Absorption: Z > Y >> X.
Chemistry of Tuhualite
Mindat Formula:
NaFe2+Fe3+Si6O15
Na may be replaced by minor K.
Na may be replaced by minor K.
Element Weights:
Elements listed:
Common Impurities:
Ti,Zr,Al,Mn,Mg,Ca,F,Cl,H2O
Crystallography of Tuhualite
Crystal System:
Orthorhombic
Class (H-M):
mmm(2/m2/m2/m) - Dipyramidal
Space Group:
Cmca
Setting:
Cmca
Cell Parameters:
a = 14.3285(8) Å, b = 17.2837(10) Å, c = 10.1202(6) Å
Ratio:
a:b:c = 0.829 : 1 : 0.586
Unit Cell V:
2,506.26 ų (Calculated from Unit Cell)
Z:
4
Morphology:
Prismatic. Forms include {100}, {010}, {001}, {110}, {111}, {011}, {021}. As tabular crystals, flattened on [100] with pyramidal terminations. Also as irregular mosslike aggregates.
Comment:
Tuhualite revisited: new crystal data and structure refinements on specimens from two localities (Mayor Island).
Crystal Structure
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Unit Cell | Unit Cell Packed
2x2x2 | 3x3x3 | 4x4x4
Unit Cell | Unit Cell Packed
2x2x2 | 3x3x3 | 4x4x4
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CIF File Best | x | y | z | a | b | c
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Data courtesy of the American Mineralogist Crystal Structure Database. Click on an AMCSD ID to view structure
| ID | Species | Reference | Link | Year | Locality | Pressure (GPa) | Temp (K) |
|---|---|---|---|---|---|---|---|
| 0015420 | Tuhualite | Merlino S (1969) Tuhualite crystal structure Science 166 1399-1401 | 1969 | Mayor Island, New Zealand | 0 | 293 |
CIF Raw Data - click here to close
X-Ray Powder Diffraction
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 7.16 Å | (100) |
| 2.766 Å | (90) |
| 3.18 Å | (80) |
| 8.62 Å | (70) |
| 5.515 Å | (70) |
| 4.85 Å | (70) |
| 4.35 Å | (70) |
Comments:
Mayor Island, New Zealand. The data are from Hutton (1956).
Geological Environment
Paragenetic Mode(s):
| Paragenetic Mode | Earliest Age (Ga) |
|---|---|
| Stage 4b: Highly evolved igneous rocks | >3.0 |
| 34 : Complex granite pegmatites | |
| 35 : Ultra-alkali and agpaitic igneous rocks |
Geological Setting:
Crystallization from magma quite impoverished in lime due to early fractionation of aegirine-hedenbergite, and perhaps aegirine-augite, in the intratelluric stage.
Type Occurrence of Tuhualite
General Appearance of Type Material:
"Relatively large grains."
Place of Conservation of Type Material:
Geological Survey of New Zealand, Lower Hutt, New Zealand, P2077; National Museum of Natural History, Washington, D.C., USA, 96879, 96880, 103053, 136507.
Geological Setting of Type Material:
In rhyolites.
Associated Minerals at Type Locality:
Other Language Names for Tuhualite
Relationship of Tuhualite to other Species
Member of:
Other Members of Tuhualite Group:
| Emeleusite | Li2Na4Fe2Si12O30 | Orth. mmm(2/m2/m2/m) |
| Zektzerite | LiNaZrSi6O15 | Orth. mmm(2/m2/m2/m) : Cmca |
Common Associates
Associations Based on Photo Data:
| 7 photos of Tuhualite associated with Aegirine | NaFe3+Si2O6 |
| 2 photos of Tuhualite associated with Quartz | SiO2 |
| 2 photos of Tuhualite associated with Aenigmatite | Na4[Fe2+10Ti2]O4[Si12O36] |
| 1 photo of Tuhualite associated with Sogdianite | K◻2Zr2Li3[Si12O30] |
| 1 photo of Tuhualite associated with Polylithionite | KLi2Al(Si4O10)(F,OH)2 |
| 1 photo of Tuhualite associated with 'Chalcedony' | SiO2 |
| 1 photo of Tuhualite associated with 'Anorthoclase' | (Na,K)AlSi3O8 |
Related Minerals - Strunz-mindat Grouping
| 9.DN. | Letnikovite-(Ce) | (Na◻)Ca2Ce2[Si7O17(OH)]F4(H2O)4 |
| 9.DN.05 | Zektzerite | LiNaZrSi6O15 |
| 9.DN.05 | Emeleusite | Li2Na4Fe2Si12O30 |
| 9.DN.10 | Semenovite-(Ce) | Na8Ca2FeBe6Ce2Si14O40(OH)4F4 |
| 9.DN.15 | Ashcroftine-(Y) | K5Na5(Y,Ca)12Si28O70(OH)2(CO3)8 · 8H2O |
| 9.DN.15 | 'Ashcroftine-(Ce)' | K5Na5(Ce,Ca)12Si28O70(OH)2(CO3)8 · 8H2O |
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 Tuhualite
mindat.org URL:
https://www.mindat.org/min-4045.html
Please feel free to link to this page.
Please feel free to link to this page.
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References for Tuhualite
Reference List:
Hutton, C. Osborne (1956) Re-examination of the mineral tuhualite. Mineralogical Magazine and Journal of the Mineralogical Society, 31 (232) 96-106 doi:10.1180/minmag.1956.031.232.07
Merlino, S. (1969) Tuhualite Crystal Structure. Science, 166 (3911). 1399-1401 doi:10.1126/science.166.3911.1399
Localities for Tuhualite
Showing 8 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.
Italy | |
| Bagiński et al. (2018) |
| Bagiński et al. (2018) | |
Mongolia | |
| Irina A. Andreeva data +1 other reference |
New Zealand (TL) | |
| Marshall (1932) +6 other references |
| NZJGG | |
| NZJGG | |
| NZJGG | |
Tajikistan | |
| L.A. Pautov data |
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Mayor Island, Bay of Plenty Region, New Zealand