Steacyite
A valid IMA mineral species
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About Steacyite
Harold Robert Steacy
Formula:
K0.3(Na,Ca)2ThSi8O20
Colour:
Gray, dark brown, green, beige
Lustre:
Vitreous, Greasy, Dull
Hardness:
5
Specific Gravity:
2.95
Crystal System:
Tetragonal
Member of:
Name:
Named in 1982 by Guy Perrault and Jan T. Szymaňski in honor of Harold Robert Steacy [June 7, 1923 Ottawa, Ontario, Canada - April 7, 2012 Ottawa, Ontario, Canada], mineralogist, former Curator of the National Mineral Collection, Geological Survey of Canada, for his contributions to Canadian mineralogy.
This page provides mineralogical data about Steacyite.
Unique Identifiers
Mindat ID:
3754
Long-form identifier:
mindat:1:1:3754:5
IMA Classification of Steacyite
Classification of Steacyite
9.CH.10
9 : SILICATES (Germanates)
C : Cyclosilicates
H : [Si4O12]8- 4-membered double rings
9 : SILICATES (Germanates)
C : Cyclosilicates
H : [Si4O12]8- 4-membered double rings
63.1.1.1
63 : CYCLOSILICATES Condensed Rings
1 : Condensed Rings (Steacyite group)
63 : CYCLOSILICATES Condensed Rings
1 : Condensed Rings (Steacyite group)
14.16.15
14 : Silicates not Containing Aluminum
16 : Silicates of U
14 : Silicates not Containing Aluminum
16 : Silicates of U
Mineral Symbols
As of 2021 there are now IMA–CNMNC approved mineral symbols (abbreviations) for each mineral species, useful for tables and diagrams.
Please only use the official IMA–CNMNC symbol. Older variants are listed for historical use only.
Please only use the official IMA–CNMNC symbol. Older variants are listed for historical use only.
| Symbol | Source | Reference for Standard |
|---|---|---|
| Scy | IMA–CNMNC | Warr, L.N. (2021). IMA–CNMNC approved mineral symbols. Mineralogical Magazine, 85(3), 291-320. doi:10.1180/mgm.2021.43 |
| Stc | The Canadian Mineralogist (2019) | The Canadian Mineralogist (2019) The Canadian Mineralogist list of symbols for rock- and ore-forming minerals (December 30, 2019). download |
Physical Properties of Steacyite
Vitreous, Greasy, Dull
Transparency:
Translucent, Opaque
Colour:
Gray, dark brown, green, beige
Hardness:
5 on Mohs scale
Cleavage:
None Observed
Density:
2.95 g/cm3 (Measured) 3.32 g/cm3 (Calculated)
Comment:
Measured on porous material.
Optical Data of Steacyite
Type:
Uniaxial (-)
RI values:
nω = 1.573 nε = 1.572
Max. Birefringence:
δ = 0.001
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:
Moderate (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 uniaxial interference figure - the conoscopic
(convergent-light, Bertrand-lens-in) view, for a grain cut with the optic axis
centred and vertical. The coloured rings are isochromatics, computed with the
same physics as the Michel-Lévy bar above; the dark cross is the isogyre.
For a genuinely uniaxial mineral viewed this way, that cross stays perfectly stationary if you rotate the stage - unlike a biaxial mineral, where it splits apart on rotation. That invariance is itself the standard diagnostic test for telling uniaxial and biaxial minerals apart at the microscope.
For a genuinely uniaxial mineral viewed this way, that cross stays perfectly stationary if you rotate the stage - unlike a biaxial mineral, where it splits apart on rotation. That invariance is itself the standard diagnostic test for telling uniaxial and biaxial minerals apart at the microscope.
Chemistry of Steacyite
Mindat Formula:
K0.3(Na,Ca)2ThSi8O20
Element Weights:
Common Impurities:
As,Mn,Pb,F,P
Crystallography of Steacyite
Crystal System:
Tetragonal
Class (H-M):
4/mmm(4/m2/m2/m) - Ditetragonal Dipyramidal
Space Group:
P4/mcc
Setting:
P4/mcc
Cell Parameters:
a = 7.58 Å, c = 14.76 Å
Ratio:
a:c = 1 : 1.947
Unit Cell V:
848.06 ų (Calculated from Unit Cell)
Morphology:
Prismatic habit, elongated along [001] and showing the forms {100} and {001} which may occasionally also display the form {110}, is the most common. A more rare habit is a dipyramidal habit showing {100}, {001) and {101}.
Twinning:
Cruciform, by 90° rotation about [010].
Crystal Structure
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Unit Cell | Unit Cell Packed
2x2x2 | 3x3x3 | 4x4x4
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2x2x2 | 3x3x3 | 4x4x4
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CIF File Best | x | y | z | a | b | c
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Stop | Start
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Labels
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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) |
|---|---|---|---|---|---|---|---|
| 0018511 | Steacyite | Prichard P, Perrault G (1972) Structure cristalline de l'ekanite de St-Hilaire, P.Q. Acta Crystallographica B28 1994-1999 |  | 1972 | Mont St-Hilaire, Quebec, Canada | 0 | 293 |
CIF Raw Data - click here to close
X-Ray Powder Diffraction
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 3.38 Å | (100) |
| 3.32 Å | (55) |
| 5.30 Å | (45) |
| 2.64 Å | (41) |
| 2.00 Å | (26) |
| 1.82 Å | (20) |
| 2.16 Å | (19) |
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 |
Type Occurrence of Steacyite
General Appearance of Type Material:
Elongated crystals to 2 mm.
Place of Conservation of Type Material:
Ecole Polytechnique, Montreal, Quebec, Canada, number 12480.
Canadian Geological Survey, Ottawa, Ontario, Canada, number 61529.
Canadian Museum of Nature, Ottawa, Canada.
National Museum of Natural History, Washington, D.C., USA, number 149820.
The Natural History Museum, London, England, number 1970,168.
Canadian Geological Survey, Ottawa, Ontario, Canada, number 61529.
Canadian Museum of Nature, Ottawa, Canada.
National Museum of Natural History, Washington, D.C., USA, number 149820.
The Natural History Museum, London, England, number 1970,168.
Geological Setting of Type Material:
In pegmatite veins in nepheline syenite.
Associated Minerals at Type Locality:
Synonyms of Steacyite
Other Language Names for Steacyite
Relationship of Steacyite to other Species
Member of:
Other Members of Steacyite Group:
| Arapovite | (K1-x◻x)(Ca,Na)2U4+Si8O20 (x ~ 0.5) | Tet. 4/mmm(4/m2/m2/m) : P4/mcc |
| Iraqite-(La) | KCa2(La,Ce,Th)Si8O20 | Tet. 4/mmm(4/m2/m2/m) : P4/mcc |
| Turkestanite | (K,◻)(Ca,Na)2ThSi8O20 · nH2O | Tet. 4/mmm(4/m2/m2/m) : P4/mcc |
Common Associates
Associations Based on Photo Data:
| 51 photos of Steacyite associated with Aegirine | NaFe3+Si2O6 |
| 51 photos of Steacyite associated with Charoite | (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 · ~3H2O |
| 15 photos of Steacyite associated with Quartz | SiO2 |
| 11 photos of Steacyite associated with Galena | PbS |
| 9 photos of Steacyite associated with Pectolite | NaCa2Si3O8(OH) |
| 5 photos of Steacyite associated with Microcline | K(AlSi3O8) |
| 4 photos of Steacyite associated with Frankamenite | K3Na3Ca5(Si12O30)(F,OH)4 · H2O |
| 3 photos of Steacyite associated with Gjerdingenite-Na | K2Na(Nb,Ti)4(Si4O12)2(OH,O)4 · 5H2O |
| 2 photos of Steacyite associated with Leucosphenite | BaNa4Ti2B2Si10O30 |
| 2 photos of Steacyite associated with Native Copper | Cu |
Related Minerals - Strunz-mindat Grouping
| 9.CH.05 | Khvorovite | (Pb,Ba,K)4Ca2[Si8B2(Si,B)2O28]F |
| 9.CH.05 | Guastoniite-(Y) | Pb4(YCa)(Si8B4O28)F |
| 9.CH.05 | Kapitsaite-(Y) | (Ba,K,Pb)4(Y,Ca)2Si8(B,Si)4O28F |
| 9.CH.05 | Hyalotekite | (Ba,Pb,K)4(Ca,Y)2(B,Be)2(Si,B)2Si8O28(F,Cl) |
| 9.CH.05 | Itsiite | Ba4Ca2[Si8B4O28]◻ |
| 9.CH.10 | Arapovite | (K1-x◻x)(Ca,Na)2U4+Si8O20 (x ~ 0.5) |
| 9.CH.10 | Turkestanite | (K,◻)(Ca,Na)2ThSi8O20 · nH2O |
| 9.CH.10 | Iraqite-(La) | KCa2(La,Ce,Th)Si8O20 |
Radioactivity
Radioactivity:
| Element | % Content | Activity (Bq/kg) | Radiation Type |
|---|---|---|---|
| Uranium (U) | 0.0000% | 0 | α, β, γ |
| Thorium (Th) | 27.8083% | 1,112,332 | α, β, γ |
| Potassium (K) | 1.4057% | 436 | 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
Other Information
Notes:
Radioactive. Emits α and β particles, but not γ radiation.
Health Risks:
No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.
Steacyite in petrology
An essential component of rock names highlighted in red, an accessory component in rock names highlighted in green.
Internet Links for Steacyite
mindat.org URL:
https://www.mindat.org/min-3754.html
Please feel free to link to this page.
Please feel free to link to this page.
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External Links:
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References for Steacyite
Reference List:
Perrault, G., Szymański, J. T. (1982) Steacyite, a new name and a re-evaluation of the nomenclature of "ekanite"-group minerals. The Canadian Mineralogist, 20 (1) 59-63
Szymański, J. T., Owens, D. R., Roberts, A. C., Ansell, H. G., Chao, G. Y. (1982) A mineralogical study and crystal structure determination of nonmetamict ekanite ThCa2Si8O20. The Canadian Mineralogist, 20 (1) 65-75
Stachowicz, M.; Bagiński, B.; Harlov, D. E.; Jokubauskas, P.; Kotowski, J.; Matyszczak, W.; Dąbrowska, A.; Macdonald, R. (2025) Multidisciplinary study of thorium mobility: formation of turkestanite and steacyite analogues, and structural insights using an XRD-directed microcrystal preparation technique. Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials, 81 (4). 418-426 doi:10.1107/s2052520625004822
Localities for Steacyite
Showing 16 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.
Canada (TL) | |
| Perrault et al. (1982) +3 other references |
Germany | |
| Blaß et al. (1994) |
Greenland | |
| - (n.d.) |
Guinea | |
| Parodi et al. (1987) |
| Parodi et al. (1987) +4 other references | |
Namibia | |
| Joachim Esche collection (SEM-EDS-analysed) +3 other references |
Portugal | |
| Chiappino et al. (2015) |
| Alves (n.d.) |
Russia | |
| Konev et al. (1996) |
| Kaneva +3 other references | |
| Pavel M. Kartashov (n.d.) +1 other reference | |
| Kaneva +3 other references | |
| Pekov et al. (2004) |
USA | |
| Minerological Record 18: 361n | |
| Robin D. Tibbit (deceased) |
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Poudrette quarry, Mont Saint-Hilaire, La Vallée-du-Richelieu RCM, Montérégie, Québec, Canada