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Dalyite
A valid IMA mineral species - grandfathered
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About Dalyite
Reginald Aldworth Daly
Formula:
K2ZrSi6O15
Colour:
Colourless, brown
Lustre:
Vitreous
Hardness:
7½
Specific Gravity:
2.82
Crystal System:
Triclinic
Member of:
Name:
Named by RenĆ© van Tassel (1916-2013) in 1952 for Reginald Aldworth Daly (18 March 1871, Napanee, Ontario, Canada ā 19 September 1957, Cambridge, Massachusetts, USA). Daly was a professor at Harvard University and was one of the most brilliant igneous petrologists and established many geological principles. There are Daly Craters on both the Moon and Mars named in his honor. He also contributed greatly to the geological structure and petrology of Ascension Island, the type locality.
Dalyite from Terceira ignimbrites contains some Na and minor Hf and Ti, but does not readily incorporate Fe, Mg and Ba.
Unique Identifiers
Mindat ID:
1214
Long-form identifier:
mindat:1:1:1214:6
Similar Names
| Dellaite | A valid IMA mineral species | Ca6Si3O11(OH)2 |
IMA Classification of Dalyite
Approved, 'Grandfathered' (first described prior to 1959)
IMA Formula:
K2Zr4+Si6O15
First published:
1952
Classification of Dalyite
9.EA.25
9 : SILICATES (Germanates)
E : Phyllosilicates
A : Single nets of tetrahedra with 4-, 5-, (6-), and 8-membered rings
9 : SILICATES (Germanates)
E : Phyllosilicates
A : Single nets of tetrahedra with 4-, 5-, (6-), and 8-membered rings
72.2.1.1
72 : PHYLLOSILICATES Two-Dimensional Infinite Sheets with Other Than Six-Membered Rings
2 : Two-Dimensional Infinite Sheets with Other Than Six-Membered Rings with 4-, 6-, and 8-membered rings
72 : PHYLLOSILICATES Two-Dimensional Infinite Sheets with Other Than Six-Membered Rings
2 : Two-Dimensional Infinite Sheets with Other Than Six-Membered Rings with 4-, 6-, and 8-membered rings
14.10.14
14 : Silicates not Containing Aluminum
10 : Silicates of Zr or Hf
14 : Silicates not Containing Aluminum
10 : Silicates of Zr or Hf
Mineral Symbols
As of 2021 there are now IMAāCNMNC approved mineral symbols (abbreviations) for each mineral species, useful for tables and diagrams.
| Symbol | Source | Reference for Standard |
|---|---|---|
| Dly | IMAāCNMNC | Warr, L.N. (2021). IMAāCNMNC approved mineral symbols. Mineralogical Magazine, 85(3), 291-320. doi:10.1180/mgm.2021.43 |
Physical Properties of Dalyite
Vitreous
Transparency:
Transparent, Translucent
Colour:
Colourless, brown
Streak:
White
Hardness:
7½ on Mohs scale
Tenacity:
Brittle
Cleavage:
Distinct/Good
Distinct on {101} and {010}, indistinct on {100}.
Distinct on {101} and {010}, indistinct on {100}.
Density:
2.82(2) g/cm3 (Measured) 2.81 g/cm3 (Calculated)
Optical Data of Dalyite
Type:
Biaxial (-)
RI values:
nα = 1.575(2) nβ = 1.590(2) nγ = 1.601(2)
2V:
Measured: 72° (2), Calculated: 80°
Max. Birefringence:
δ = 0.026
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 Āµm 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 Āµm 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 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:
Very weak, r > v
Optical Extinction:
X ā§ c = 7Ā°.
Chemistry of Dalyite
Mindat Formula:
K2ZrSi6O15
Element Weights:
Elements listed:
Common Impurities:
Ti,Al,Fe,Mn,Mg,Ca,Ba,P
Chemical Analysis
Oxide wt%:
| 1 | 2 | |
|---|---|---|
| SiO2 | 63.07 % | 61.85 % |
| Al2O3 | 0.06 % | |
| TiO2 | 1.23 % | |
| ZrO2 | 19.37 % | 21.70 % |
| CaO | 0.02 % | |
| MgO | 0.10 % | |
| MnO | 0.02 % | |
| FeO | 0.28 % | |
| K2O | 15.60 % | 14.60 % |
| Na2O | 0.04 % | 1.75 % |
| BaO | 0.11 % | |
| P2O5 | 0.04 % | |
| Fe2O3 | 0.37 % | |
| H2O | 0.64 % | |
| Total: | 99.94 % | 100.91 % |
Sample references:
| ID | Type | Locality | Reference | Notes |
|---|---|---|---|---|
| 1 | Heilefjellet dikes, Dalsfjorden, Askvoll, Vestland, Norway | Means of 10 analysis of individual point analyses of 5 crystals. | ||
| 2 | Type Specimen | Green Mountain, Ascension Island, Saint Helena, Ascension and Tristan da Cunha | Analysis by Dr. M. H. Hey |
Crystallography of Dalyite
Crystal System:
Triclinic
Class (H-M):
1 - Pinacoidal
Space Group:
P1
Cell Parameters:
a = 7.371(3) Å, b = 7.730(3) Å, c = 6.912(3) Å
α = 106.23(3)°, β = 111.45(3)°, γ = 100.00(3)°
α = 106.23(3)°, β = 111.45(3)°, γ = 100.00(3)°
Ratio:
a:b:c = 0.954 : 1 : 0.894
Unit Cell V:
334.76 Ć
Ā³ (Calculated from Unit Cell)
Z:
1
Morphology:
Short prismatic. Dominated by {101} and pinacoids parallel to [001].
Twinning:
Not uncommon, with {100} as the composition plane.
Crystal Structure
Load
Unit Cell | Unit Cell Packed
2x2x2 | 3x3x3 | 4x4x4
Unit Cell | Unit Cell Packed
2x2x2 | 3x3x3 | 4x4x4
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Big Balls | Small Balls | Just Balls | Spacefill
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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) |
|---|---|---|---|---|---|---|---|
| 0010622 | Dalyite | Fleet S G (1965) The crystal structure of dalyite Zeitschrift fur Kristallographie 121 349-368 |  | 1965 | 0 | 293 |
CIF Raw Data - click here to close
X-Ray Powder Diffraction
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 4.20 Ć | (vs) |
| 3.58 Ć | (vs) |
| 3.08 Ć | (vs) |
| 5.90 Ć | (s) |
| 4.31 Ć | (s) |
| 6.54 Ć | (m) |
| 3.36 Ć | (m) |
Geological Environment
Paragenetic Mode(s):
| Paragenetic Mode | Earliest Age (Ga) |
|---|---|
| Stage 3a: Earthās earliest Hadean crust | >4.50 |
| 9 : Lava/xenolith minerals (hornfels, sanidinite facies) | |
| Stage 4b: Highly evolved igneous rocks | >3.0 |
| 35 : Ultra-alkali and agpaitic igneous rocks |
Type Occurrence of Dalyite
General Appearance of Type Material:
Colorless, prismatic crystals to 0.5 mm.
Place of Conservation of Type Material:
The Natural History Museum, London, England, 64685.
National Museum of Natural History, Washington, D.C., USA, 113106.
National Museum of Natural History, Washington, D.C., USA, 113106.
Geological Setting of Type Material:
Ejected blocks of alkalic granite in trachytic and basaltic tuffs.
Associated Minerals at Type Locality:
Other Language Names for Dalyite
Relationship of Dalyite to other Species
Member of:
Other Members of Dalyite Group:
| Davanite | K2TiSi6O15 | Tric. |
| Sazhinite-(Ce) | Na3CeSi6O15 Ā· 2H2O | Orth. mm2 : Pmm2 |
| Sazhinite-(La) | Na3La[Si6O15] Ā· 2H2O | Orth. mm2 : Pmm2 |
Common Associates
Associations Based on Photo Data:
| 7 photos of Dalyite associated with Chevkinite-(Ce) | Ce4(Ti,Fe2+,Fe3+)5O8(Si2O7)2 |
| 3 photos of Dalyite associated with Vlasovite | Na2ZrSi4O11 |
| 3 photos of Dalyite associated with Astrophyllite | K2NaFe2+7Ti2[Si4O12]2O2(OH)4F |
| 3 photos of Dalyite associated with Alkali Feldspar | |
| 2 photos of Dalyite associated with Janhaugite | (Na,Ca)3(Mn2+,Fe2+)3(Ti,Zr,Nb)2(Si2O7)2O2(OH,F)2 |
| 1 photo of Dalyite associated with Britholite Group | (REE,Ca)5[(Si,P)O4]3X |
| 1 photo of Dalyite associated with Zircon | Zr(SiO4) |
| 1 photo of Dalyite associated with Aegirine | NaFe3+Si2O6 |
| 1 photo of Dalyite associated with Quartz | SiO2 |
| 1 photo of Dalyite associated with Feldspar Group |
Related Minerals - Strunz-mindat Grouping
| 9.EA. | Hydroxymcglassonite-(K) | KSr4Si8O20(OH) Ā· 8H2O |
| 9.EA. | Miyawakiite-(Y) | ā»Y4Fe2(Si8O20)(CO3)4(H2O)3 |
| 9.EA. | Bussyite-(Y) | (Y,REE,Ca)3(Na,Ca)6MnSi9Be5(O,OH,F)34 |
| 9.EA. | Hydroxyapophyllite-(NH4) | (NH4)Ca4(Si8O20)(OH)(H2O)8 |
| 9.EA. | Fluorapophyllite-(NH4) | NH4Ca4(Si8O20)F Ā· 8H2O |
| 9.EA.05 | Gillespite | BaFe2+Si4O10 |
| 9.EA.05 | Cuprorivaite | CaCuSi4O10 |
| 9.EA.05 | Wesselsite | SrCuSi4O10 |
| 9.EA.05 | Effenbergerite | BaCuSi4O10 |
| 9.EA.07 | Fluorapophyllite-(Cs) | CsCa4(Si8O20)F Ā· 8H2O |
| 9.EA.10 | Ekanite | Ca2ThSi8O20 |
| 9.EA.15 | Fluorapophyllite-(Na) | NaCa4(Si8O20)F Ā· 8H2O |
| 9.EA.15 | Fluorapophyllite-(K) | KCa4(Si8O20)(F,OH) Ā· 8H2O |
| 9.EA.15 | Hydroxyapophyllite-(K) | KCa4(Si8O20)(OH,F) Ā· 8H2O |
| 9.EA.20 | Magadiite | Na2Si14O29 Ā· 11H2O |
| 9.EA.25 | Davanite | K2TiSi6O15 |
| 9.EA.30 | Sazhinite-(La) | Na3La[Si6O15] Ā· 2H2O |
| 9.EA.30 | Sazhinite-(Ce) | Na3CeSi6O15 Ā· 2H2O |
| 9.EA.35 | Armstrongite | CaZr[Si6O15] Ā· 3H2O |
| 9.EA.40 | Okenite | Ca10Si18O46 Ā· 18H2O |
| 9.EA.45 | Perettiite-(Y) | Y2Mn4FeSi2B8O24 |
| 9.EA.45 | Nekoite | Ca3Si6O15 Ā· 7H2O |
| 9.EA.45 | Badakhshanite-(Y) | Y2Mn4Al(Si2B7BeO24) |
| 9.EA.47 | Shlykovite | KCa[Si4O9(OH)] Ā· 3H2O |
| 9.EA.50 | Diegogattaite | Na2CaCu2Si8O20 Ā· H2O |
| 9.EA.50 | Cavansite | Ca(VO)Si4O10 Ā· 4H2O |
| 9.EA.52 | Yangite | PbMnSi3O8 Ā· H2O |
| 9.EA.55 | Pentagonite | Ca(VO)Si4O10 Ā· 4H2O |
| 9.EA.60 | Penkvilksite | Na4Ti2Si8O22 Ā· 4H2O |
| 9.EA.60 | Tumchaite | Na2Zr(Si4O11) Ā· 2H2O |
| 9.EA.65 | Nabesite | Na2BeSi4O10 Ā· 4H2O |
| 9.EA.70 | Ajoite | (K,Na)Cu7AlSi9O24(OH)6 Ā· 3H2O |
| 9.EA.75 | Zeravshanite | Na2Cs4Zr3[Si18O45]*2H2O |
| 9.EA.80 | Bussyite-(Ce) | (Ce,REE)3(Na,H2O)6MnSi9Be5(O,OH)30F4 |
| 9.EA.85 | Plumbophyllite | Pb2Si4O10 Ā· H2O |
Radioactivity
Radioactivity:
| Element | % Content | Activity (Bq/kg) | Radiation Type |
|---|---|---|---|
| Uranium (U) | 0.0000% | 0 | Ī±, Ī², Ī³ |
| Thorium (Th) | 0.0000% | 0 | Ī±, Ī², Ī³ |
| Potassium (K) | 13.5306% | 4,194 | Ī², Ī³ |
For comparison:
- Banana: ~15 Bq per fruit
- Granite: 1,000ā3,000 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 ĀµSv/year. Note that natural background radiation averages around 2400 ĀµSv/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: ā
| Distance | Dose rate | Risk |
|---|---|---|
| 1āÆcm | ||
| 10āÆcm | ||
| 1āÆm |
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:
Strongly cathodoluminescent in bright azure-blue.
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 Dalyite
mindat.org URL:
https://www.mindat.org/min-1214.html
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References for Dalyite
Reference List:
Van Tassel, R., Hey, M. H. (1952) Dalyite, a new potassium zirconium silicate, from Ascension Island, Atlantic. Mineralogical Magazine and Journal of the Mineralogical Society, 29 (217) 850-857 doi:10.1180/minmag.1952.029.217.02
Van Tassel, R., Hey, M. H. (1952) Dalyite, a new potassium zirconium silicate, from Ascension Island, Atlantic. Mineralogical Magazine and Journal of the Mineralogical Society, 29 (217) 850-857 doi:10.1180/minmag.1952.029.217.02
Fleet, S. G. (1965) The crystal structure of dalyite. Zeitschrift fĆ¼r Kristallographie, 121 (5). 349-368 doi:10.1524/zkri.1965.121.5.349
Cann, J. R. (1967) A second occurrence of dalyite and the petrology of some ejected syenite blocks from SĆ£o Miguel, Azores. Mineralogical Magazine and Journal of the Mineralogical Society, 36 (278) 227-232 doi:10.1180/minmag.1967.036.278.05
Robins, B., Furnes, H., Ryan, P. (1983) A new occurrence of dalyite. Mineralogical Magazine, 47 (342) 93-94 doi:10.1180/minmag.1983.047.342.21
Linthout, K., Nobel, F. A., Lustenhouwer, W. J. (1988) First Occurrence of Dalyite in Extrusive Rock. Mineralogical Magazine, 52 (368) 705-708 doi:10.1180/minmag.1988.052.368.16
Jeffery, A. J., Gertisser, R., Jackson, R. A., O'Driscoll, B., Kronz, A. (2016) On the compositional variability of dalyite, K2ZrSi6O15: a new occurrence from Terceira, Azores. Mineralogical Magazine, 80 (4) 547-565 doi:10.1180/minmag.2016.080.018
Imaoka, Teruyoshi, Akita, Sachiho, Nagashima, Mariko (2021) Dalyite (K2ZrSi6O15) and Zektzerite (LiNaZrSi6O15) in Aegirine-bearing Albitite from Iwagi Islet, SW Japan. Journal of Geography (Chigaku Zasshi), 130 (3) 369-378 doi:10.5026/jgeography.130.369
Dokuchits, Emilia Yu.; Jiang, Shao-Yong; Stepanov, Aleksandr S.; Zhukova, Irina A.; Radomskaya, Tatiana A.; Su, Hui-Min; Liu, Si-Qi (2023) Mineral associations and in-situ major and trace element compositions of dalyite from charoitites, Murun complex, Siberia. Ore Geology Reviews, 153. 105297 doi:10.1016/j.oregeorev.2023.105297
Localities for Dalyite
Showing 26 localities.
symbol to view information about a locality.
The Locality List
- This locality has map coordinates listed.
- This locality has estimated coordinates.
ā - 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.
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Ćgua de Pau Volcano, SĆ£o Miguel, Azores, Portugal