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Keiviite-(Y)
A valid IMA mineral species
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About Keiviite-(Y)
Formula:
Y2Si2O7
Colour:
Colorless to white
Lustre:
Vitreous
Hardness:
4 - 5
Specific Gravity:
4.45
Crystal System:
Monoclinic
Member of:
Name:
Named for its relationship to keiviite-(Yb), with Y dominant over Yb and written according to the IMA nomenclature for rare earth element minerals.
Unique Identifiers
Mindat ID:
2177
Long-form identifier:
mindat:1:1:2177:3
Similar Names
| Keiviite-(Y)-Keiviite-(Yb) Series | A solid-solution series between two end-member minerals | |
| Keiviite-(Yb) | A valid IMA mineral species | Yb2Si2O7 |
| Kievite | A synonym of Cummingtonite | |
| Kivite | A rock subtype | |
| Kivuite | A discredited species name | Th(UO2)4(PO3OH)2(OH)8 · 7H2O |
IMA Classification of Keiviite-(Y)
Approved
Approval year:
1984
First published:
1985
Classification of Keiviite-(Y)
9.BC.05
9 : SILICATES (Germanates)
B : Sorosilicates
C : Si2O7 groups, without non-tetrahedral anions; cations in octahedral [6] and greater coordination
9 : SILICATES (Germanates)
B : Sorosilicates
C : Si2O7 groups, without non-tetrahedral anions; cations in octahedral [6] and greater coordination
55.2.1a.2
55 : SOROSILICATES Si2O7 Groups,Generally with no Additional Anions
2 : Si2O7 Groups, Generally with no Additional Anions with cations in [6] coordination
55 : SOROSILICATES Si2O7 Groups,Generally with no Additional Anions
2 : Si2O7 Groups, Generally with no Additional Anions with cations in [6] coordination
14.8.2
14 : Silicates not Containing Aluminum
8 : Silicates of Group III metals other than Al
14 : Silicates not Containing Aluminum
8 : Silicates of Group III metals other than Al
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 |
|---|---|---|
| Kvi-Y | 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 Keiviite-(Y)
Vitreous
Transparency:
Transparent
Colour:
Colorless to white
Streak:
White
Hardness:
4 - 5 on Mohs scale
Hardness:
VHN20=1400 kg/mm2 - Vickers
Cleavage:
None Observed
Fracture:
Irregular/Uneven
Density:
4.45 g/cm3 (Measured) 4.48 g/cm3 (Calculated)
Optical Data of Keiviite-(Y)
Type:
Biaxial (-)
RI values:
nα = 1.713(1) nβ = 1.748(1) nγ = 1.758(1)
2V:
Measured: 55° to 56°, Calculated: 54°
Max. Birefringence:
δ = 0.045
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:
Very 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:
weak
Chemistry of Keiviite-(Y)
Mindat Formula:
Y2Si2O7
Element Weights:
Elements listed:
Crystallography of Keiviite-(Y)
Crystal System:
Monoclinic
Class (H-M):
2/m - Prismatic
Space Group:
B2/m
Setting:
C2/m
Cell Parameters:
a = 6.845(5) Å, b = 8.960(5) Å, c = 4.734(3) Å
β = 101.65(5)°
β = 101.65(5)°
Ratio:
a:b:c = 0.764 : 1 : 0.528
Unit Cell V:
284.36 ų (Calculated from Unit Cell)
Z:
2
Comment:
Space group by analogy to keiviite-(Yb)
X-Ray Powder Diffraction
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 3.23 Å | (100) |
| 4.65 Å | (90) |
| 3.04 Å | (80) |
| 2.280 Å | (70) |
| 5.40 Å | (50) |
| 2.729 Å | (50) |
| 2.692 Å | (50) |
| 1.841 Å | (50) |
| 1.685 Å | (50) |
Comments:
Mt. Ploskaya, Russia. Data from the type description.
Geological Environment
Paragenetic Mode(s):
| Paragenetic Mode | Earliest Age (Ga) |
|---|---|
| Stage 4b: Highly evolved igneous rocks | >3.0 |
| 34 : Complex granite pegmatites |
Type Occurrence of Keiviite-(Y)
General Appearance of Type Material:
Prismatic crystals, 0.05 to 1 mm long and less than 0.15 mm thick.
Place of Conservation of Type Material:
Geology Museum, Kola Branch, Academy of Sciences, Apatity, Russia, 5958/6.
Mining Institute, St. Petersburg, Russia, 1343-1/1.
A.E. Fersman Mineralogical Museum, Academy of Sciences, Moscow, Russia.
Mining Institute, St. Petersburg, Russia, 1343-1/1.
A.E. Fersman Mineralogical Museum, Academy of Sciences, Moscow, Russia.
Geological Setting of Type Material:
Amazonite pegmatites.
Associated Minerals at Type Locality:
Høgetveit Feldspar Quarries, Evje og Hornnes, Agder, Norway