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Indialite
A valid IMA mineral species - grandfathered
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About Indialite
Flag of India
Formula:
Mg2Al3(AlSi5O18)
Colour:
Colourless (thin section).
Lustre:
Vitreous
Hardness:
7 - 7½
Specific Gravity:
2.512
Crystal System:
Hexagonal
Member of:
Name:
Named by A. Miyashiro and T. Iiyama in 1954 after the country of India, where the type locality is located.
Type Locality:
Dimorph of:
The Mg analogue of ferroindialite.
The hexagonal high-temperature dimorph of cordierite (orthorhombic-pseudohexagonal).
Note: the formula has also been expressed as Al2SiMg2[Al2Si4]O18 (Pezzotta, 2005), and the mineral has been assigned to the beryl group.
Material at the type locality was anthropogenic (no longer treated this way, though) since it was formed as the result of fusion and recrystallization of rocks above burning coal seams. It was subsequently found in nature in hornfels, and rapidly quenched volcanic rocks.
The hexagonal high-temperature dimorph of cordierite (orthorhombic-pseudohexagonal).
Note: the formula has also been expressed as Al2SiMg2[Al2Si4]O18 (Pezzotta, 2005), and the mineral has been assigned to the beryl group.
Material at the type locality was anthropogenic (no longer treated this way, though) since it was formed as the result of fusion and recrystallization of rocks above burning coal seams. It was subsequently found in nature in hornfels, and rapidly quenched volcanic rocks.
Unique Identifiers
Mindat ID:
2026
Long-form identifier:
mindat:1:1:2026:4
Similar Names
IMA Classification of Indialite
Approved, 'Grandfathered' (first described prior to 1959)
IMA Formula:
Mg2Al3(Si5AlO18)
Classification of Indialite
9.CJ.05
9 : SILICATES (Germanates)
C : Cyclosilicates
J : [Si6O18]12- 6-membered single rings (sechser-Einfachringe), without insular complex anions
9 : SILICATES (Germanates)
C : Cyclosilicates
J : [Si6O18]12- 6-membered single rings (sechser-Einfachringe), without insular complex anions
61.1.1.3
61 : CYCLOSILICATES Six-Membered Rings
1 : Six-Membered Rings with [Si6O18] rings; possible (OH) and Al substitution
61 : CYCLOSILICATES Six-Membered Rings
1 : Six-Membered Rings with [Si6O18] rings; possible (OH) and Al substitution
16.19.1
16 : Silicates Containing Aluminum and other Metals
19 : Aluminosilicates of Fe and Mg
16 : Silicates Containing Aluminum and other Metals
19 : Aluminosilicates of Fe and Mg
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 |
|---|---|---|
| Ind | 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 Indialite
Vitreous
Transparency:
Transparent
Colour:
Colourless (thin section).
Hardness:
7 - 7½ on Mohs scale
Density:
2.512 g/cm3 (Measured) 2.59 g/cm3 (Calculated)
Comment:
Measured values on artificial material.
Optical Data of Indialite
Type:
Uniaxial (-)
RI values:
nω = 1.539 nε = 1.534
Max. Birefringence:
δ = 0.005
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:
None to Very Low
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 Indialite
Mindat Formula:
Mg2Al3(AlSi5O18)
Element Weights:
Elements listed:
Common Impurities:
Fe,Mn,Na
Crystallography of Indialite
Crystal System:
Hexagonal
Class (H-M):
6/mmm(6/m2/m2/m) - Dihexagonal Dipyramidal
Space Group:
P6/mcc
Cell Parameters:
a = 9.8 Å, c = 9.345 Å
Ratio:
a:c = 1 : 0.954
Unit Cell V:
777.25 ų (Calculated from Unit Cell)
Z:
2
Morphology:
Small hexagonal grains and clusters of spiral-shaped grains, some exhibiting tentacles or multiple terminations.
Crystal Structure
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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) |
|---|---|---|---|---|---|---|---|
| 0001448 | Indialite | Daniels P (1992) Structural effects of the incorporation of large-radius alkalis in high cordierite American Mineralogist 77 407-411 |  | 1992 | synthetic | 0 | 293 |
| 0005136 | Indialite | Meagher E P, Gibbs G V (1977) The polymorphism of cordierite: II. The crystal structure of indialite The Canadian Mineralogist 15 43-49 | | 1977 | from a burning coal seam in the Bokaro coalfield, India | 0 | 293 |
| 0003187 | Indialite | Balassone G, Franco E, Mattia C A, Puliti R (2004) Indialite in xenolithic rocks from Somma-Vesuvius volcano (Southern Italy): Crystal chemistry and petrogenetic features American Mineralogist 89 1-6 | | 2004 | 0 | 293 | |
| 0007855 | Indialite | Schwartz K B, Leong D B, McConville R L (1994) Structural chemistry of synthetic cordierite: evidence for solid solutions and disordered compositional domains in Bi-flux-grown Mg-cordierites Physics and Chemistry of Minerals 20 563-574 | 1994 | 0 | 293 | ||
| 0007853 | Indialite | Schwartz K B, Leong D B, McConville R L (1994) Structural chemistry of synthetic cordierite: evidence for solid solutions and disordered compositional domains in Bi-flux-grown Mg-cordierites Physics and Chemistry of Minerals 20 563-574 | 1994 | 0 | 293 |
CIF Raw Data - click here to close
X-Ray Powder Diffraction
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 8.48 Å | (100) |
| 3.027 Å | (85) |
| 3.138 Å | (65) |
| 3.379 Å | (55) |
| 4.094 Å | (50) |
| 4.89 Å | (30) |
| 1.6882 Å | (30) |
Comments:
Obtained on artificial material.
Geological Environment
Paragenetic Mode(s):
| Paragenetic Mode | Earliest Age (Ga) |
|---|---|
| Stage 2: Planetesimal differentiation and alteration | 4.566-4.550 |
| 6 : Secondary asteroid phases | 4.566-4.560 |
| Stage 7: Great Oxidation Event | <2.4 |
| 45b : [Other oxidized fumarolic minerals] | |
| Stage 10a: Neoproterozoic oxygenation/terrestrial biosphere | <0.6 |
| 50 : Coal and/or oil shale minerals | <0.36 |
| Stage 10b: Anthropogenic minerals | <10 Ka |
| 54 : Coal and other mine fire minerals (see also #51 and #56) |
Geological Setting:
Polymetamorphosed pelitic rock (Japan); volcanic eruptive matter (Bellerberg volcano).
Type Occurrence of Indialite
Geological Setting of Type Material:
Burning coal seam underlying sedimentary rocks
Associated Minerals at Type Locality:
Nickenicher Weinberg, Nickenich, Pellenz, Mayen-Koblenz, Rhineland-Palatinate, Germany