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Chloritoid

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Formula:
(Fe2+,Mg,Mn2+)Al2(SiO4)O(OH)2
System:
Monoclinic
Colour:
dark green to green-gray ...
Hardness:
Name:
Named in 1837 by Gustav Rose for the visual similarity to chlorite-group minerals.
Carboirite-Chloritoid Series. The Fe2+ analogue of Magnesiochloritoid.

Monoclinic and triclinic polytypes are known.

Classification of Chloritoid

Approved
9.AF.85

9 : SILICATES (Germanates)
A : Nesosilicates
F : Nesosilicates with additional anions; cations in [4], [5] and/or only [6] coordination
52.3.3.1

52 : NESOSILICATES Insular SiO4 Groups and O,OH,F,H2O
3 : Insular SiO4 Groups and O, OH, F, and H2O with cations in [6] coordination only
16.19.6

16 : Silicates Containing Aluminum and other Metals
19 : Aluminosilicates of Fe and Mg
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First Recorded Occurrence of Chloritoid

Physical Properties of Chloritoid

Vitreous, Pearly
Diaphaneity (Transparency):
Translucent
Colour:
dark green to green-gray or nearly black.
Hardness (Mohs):
Cleavage:
Perfect
{001} perfect, {110} good.
Density:
3.4 - 3.8 g/cm3 (Measured)    

Crystallography of Chloritoid

Crystal System:
Monoclinic
Class (H-M):
2/m - Prismatic
Space Group:
B2/b
Space Group Setting:
C2/c
Cell Parameters:
a = 9.50Å, b = 5.50Å, c = 18.22Å
β = 101.9°
Ratio:
a:b:c = 1.727 : 1 : 3.313
Unit Cell Volume:
V 931.54 ų (Calculated from Unit Cell)
Z:
4
Morphology:
Thin to thick foliated plates or as massive aggremates. Seldom as pseudohexagonal tabular crystals.

Also triclinic.
Twinning:
Common on {001}, polysynthetic.
Comment:
For monoclinic polytype (space group C2/c). Triclinic polytype (C-1) has a = 9.46(1), b = 5.50(1), c = 9.15(1) A, α = 97.05(2), β = 101.56(2), γ = 90.10(2)°.
X-Ray Powder Diffraction Data:
d-spacingIntensity
4.46 (100)
2.964 (18)
2.459 (6)
2.356 (7)
2.306 (14)
1.574 (11)
1.482 (6)

Optical Data of Chloritoid

Type:
Biaxial (+)
RI values:
nα = 1.713 - 1.730 nβ = 1.719 - 1.734 nγ = 1.723 - 1.740
2V:
Measured: 36° to 89°, Calculated: 78° to 80°
Max Birefringence:
δ = 0.010
Image shows birefringence interference colour range (at 30µm thickness) and does not take into account mineral colouration.
Surface Relief:
High
Dispersion:
r > v

Chemical Properties of Chloritoid

Formula:
(Fe2+,Mg,Mn2+)Al2(SiO4)O(OH)2
Essential elements:
All elements listed in formula:

Relationship of Chloritoid to other Species

Series:
Forms a series with Carboirite (see here)
Other Members of Group:
CarboiriteFeAl2(GeO4)O(OH)2
MagnesiochloritoidMgAl2(SiO4)O(OH)2
Ottrélite(Mn2+,Fe2+,Mg)Al2(SiO4)O(OH)2
9.AF.05SillimaniteAl2(SiO4)O
9.AF.10AndalusiteAl2(SiO4)O
9.AF.10KanonaiteMn3+Al(SiO4)O
9.AF.15KyaniteAl2(SiO4)O
9.AF.20MulliteAl4+2xSi2-2xO10-x
9.AF.20Krieselite(Al,Ga)2(GeO4)(OH)2
9.AF.23BoromulliteAl9BSi2O19
9.AF.25YoderiteMg(Al,Fe3+)3(SiO4)2O(OH)
9.AF.30Magnesiostaurolite(Mg,Li,Fe2+)1.5-2Al9(SiO4)4O6(OH)2
9.AF.30Staurolite(Fe2+,Mg,Zn)1.5-2Al9(SiO4)4O6(OH,O)2
9.AF.30Zincostaurolite(Zn,Li,Fe2+,Mg)1.5-2Al9(SiO4)4O6(OH)2
9.AF.35TopazAl2(SiO4)(F,OH)2
9.AF.40NorbergiteMg3(SiO4)(F,OH)2
9.AF.45AlleghanyiteMn52+(SiO4)2(OH)2
9.AF.45Chondrodite(Mg,Fe2+)5(SiO4)2(F,OH)2
9.AF.45ReinhardbraunsiteCa5(SiO4)2(OH,F)2
9.AF.45KumtyubeiteCa5(SiO4)2F2
9.AF.45HydroxylchondroditeMg5(SiO4)2(OH)2
9.AF.50Humite(Mg,Fe2+)7(SiO4)3(F,OH)2
9.AF.50Manganhumite(Mn2+,Mg)7(SiO4)3(OH)2
9.AF.50Unnamed (Ca-analogue of Humite)Ca7(SiO4)4F2
9.AF.55ClinohumiteMg9(SiO4)4F2
9.AF.55SonoliteMn92+(SiO4)4(OH,F)2
9.AF.55HydroxylclinohumiteMg9(SiO4)4(OH)2
9.AF.60LeucophoeniciteMn72+(SiO4)3(OH)2
9.AF.65Ribbeite(Mn2+,Mg)5(SiO4)2(OH)2
9.AF.70JerrygibbsiteMn92+(SiO4)4(OH)2
9.AF.75FranciscaniteMn62+(V5+,☐)2(SiO4)2(O,OH)6
9.AF.75ÖrebroiteMn32+(Sb5+,Fe3+)(SiO4)(O,OH)3
9.AF.75WeliniteMn62+(W6+,Mg)2(SiO4)2(O,OH)6
9.AF.80EllenbergeriteMg6(Mg,Ti,Zr,◻)2(Al,Mg)6Si8O28(OH)10
9.AF.85MagnesiochloritoidMgAl2(SiO4)O(OH)2
9.AF.85Ottrélite(Mn2+,Fe2+,Mg)Al2(SiO4)O(OH)2
9.AF.90PoldervaartiteCaCa[SiO3(OH)](OH)
9.AF.90OlmiiteCaMn2+[SiO3(OH)](OH)
16.19.1IndialiteMg2Al3(AlSi5O18)
16.19.2Cordierite(Mg,Fe)2Al3(AlSi5O18)
16.19.3Sekaninaite(Fe,Mg)2Al3(AlSi5O18)
16.19.4Ferro-gedrite☐{Fe22+}{Fe32+Al2}(Al2Si6O22)(OH)2
16.19.5Staurolite(Fe2+,Mg,Zn)1.5-2Al9(SiO4)4O6(OH,O)2
16.19.7AmesiteMg2Al(AlSiO5)(OH)4
16.19.8Corundophilite(Mg,Fe,Al)6(Si,Al)4O10(OH)8
16.19.9YoderiteMg(Al,Fe3+)3(SiO4)2O(OH)
16.19.10Delessite(Mg,Fe,Fe,Al)(Si,Al)4O10(O,OH)8
16.19.11Ferrocarpholite(Fe2+,Mg)Al2(Si2O6)(OH)4
16.19.12Magnesiocarpholite(Mg,Fe2+)Al2(Si2O6)(OH)4
16.19.13Chamosite(Fe2+,Mg)5Al(AlSi3O10)(OH)8
16.19.14Orthochamosite(Fe2+,Mg,Fe3+)5Al(AlSi3O10)(OH,O)8
16.19.15Berthierine(Fe2+,Fe3+,Al)3(Si,Al)2O5(OH)4
16.19.16Odinite(Fe,Mg,Al,Fe,Ti,Mn)2.4((Si,Al)2O5)(OH)4
16.19.17Clinochlore(Mg,Fe2+)5Al(AlSi3O10)(OH)8
16.19.18Gedrite☐{Mg2}{Mg3Al2}(Al2Si6O22)(OH)2
16.19.19Magnesiogedrite
16.19.20Diabantite(Mg,Fe,Al)6((Si,Al)4O10)(OH)8
16.19.21Sudoite(Mg,Fe2+)2Al3(AlSi3O10)(OH)8
16.19.22Vermiculite(Mg,Fe,Al)3((Al,Si)4O10)(OH)2 · 4H2O
16.19.23Corrensite(Mg,Fe)9((Si,Al)8O20)(OH)10 · nH2O

Other Names for Chloritoid

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.

References for Chloritoid

Reference List:
Acta Crystallographica: B31: 780.

American Mineralogist (1980): 65: 534-539.

Theye, T., Seidel, E., and Vidal, O. (1992) Carpholite, sudoite, chloritoid in low-grade high-pressure metapelites from Crete and the Peloponnese, Greece. European Journal of Mineralogy: 4: 487-507.

Theye, T. (2000) New experimental high pressure data on chloritoid and carpholite. Beiheft No. 1, European Journal of Mineralogy: 12: 212.

Internet Links for Chloritoid

Localities for Chloritoid

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