Chromdravite Mineral Data

Chromdravite Mineral Data

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General Chromdravite Information

Chemical Formula:

NaMg3(Cr,Fe+++)6(BO3)3Si6O18(OH)4

Composition:

Molecular Weight = 1,114.61 gm

Sodium 2.06 % Na 2.78 % Na₂O

Magnesium 6.54 % Mg 10.85 % MgO

Chromium 20.99 % Cr 27.45 % CrO

Iron 7.52 % Fe 10.75 % Fe₂O₃

Silicon 15.12 % Si 32.34 % SiO₂

Boron 2.91 % B 9.37 % B₂O₃

Hydrogen 0.36 % H 3.23 % H₂O

Oxygen 44.50 % O

______ ______

100.00 % 96.77 % = TOTAL OXIDE

Empirical Formula:

NaMg₃Cr_4.5Fe³⁺_1.5(BO₃)₃Si₆O₁₈(OH)₄

Environment:

Magnesium and chromium-bearing tourmaline in micaceous metasomatites.

IMA Status:

Approved IMA 1983 (Dana # Changed)

Locality:

Onezhkii depression, central Karelia, Russia. Link to MinDat.org Location Data.

Name Origin:

Named for the compositional relationship to dravite.

Synonym:

Chromdravite - (61.3.1.11)

Tourmaline

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Chromdravite Crystallography

Axial Ratios:

a:c = 1:0.45127

Cell Dimensions:

a = 16.11, c = 7.27, Z = 3; V = 1,634.02 Den(Calc)= 3.40

Crystal System:

Trigonal - Ditrigonal PyramidalH-M Symbol (3m) Space Group: R 3m

$Help on X Ray Diffraction:$ X Ray Diffraction:

By Intensity(I/I_o): 2.62(1), 3.04(0.75), 3.58(0.75),

Crystal Structure:

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Bosi F , Lucchesi S , Reznitskii L , European Journal of Mineralogy , 16 (2004) p.345-352, Crystal chemistry of the dravite-chromdravite series, Note: Tourmaline TMt3b, Locality: Sludyanka crystalline complex, Lake Baikal, Russia

View Additional jPOWD Structure files for Chromdravite
[1] [2] [3]

Physical Properties of Chromdravite

Cleavage:

None

Color:

Greenish black, Dark green.

Density:

3.4

Diaphaniety:

Translucent to Opaque

Habit:

Blocky - Crystal shape tends to be equant (e.g. feldspars).

Habit:

Striated - Parallel lines on crystal surface or cleavage face.

Hardness:

7-7.5 - Quartz-Garnet

Luminescence:

Non-fluorescent.

Luster:

Vitreous - Resinous

Streak:

greenish gray

Optical Properties of Chromdravite

Dichroism (e):

yellow green.

Dichroism (w):

dark green.

Gladstone-Dale:

CI meas= -0.029 (Excellent) - where the CI = (1-KPDmeas/KC)
CI calc= -0.029 (Excellent) - where the CI = (1-KPDcalc/KC)
KPDcalc= 0.2209,KPDmeas= 0.2209,KC= 0.2147

Optical Data:

Uniaxial (-), e=1.722-1.724, w=1.778-1.78, bire=0.0560.

Calculated Properties of Chromdravite

Electron Density:

r_electron=3.32 gm/cc
note: r_Chromdravite=3.40 gm/cc.

Fermion Index

Fermion Index = 0.04114
Boson Index = 0.95886

Photoelectric:

PE_Chromdravite= 7.71 barns/electron
U=PE_Chromdravite x r_electron= 25.62 barns/cc.

Radioactivity:

GRapi = 0 (Gamma Ray American Petroleum Institute Units)

Chromdravite is Not Radioactive

Chromdravite Classification

Dana Class:

61.3e.1.11 (61)Cyclosilicate Six-Membered Rings

(61.3e)with borate groups (Sodic Tourmaline Subgroup)

(61.3e.1)Dana Group

61.3e.1.9 Dravite! NaMg3Al6(BO3)3Si6O18(OH)4 R 3m 3m

61.3e.1.10 Schorl! NaFe3Al6(BO3)3Si6O18(OH)4 R 3m 3m

61.3e.1.11 Chromdravite ! NaMg3(Cr,Fe)6(BO3)3Si6O18(OH)4 R 3m 3m

61.3e.1.12 Vanadiumdravite! NaMg3V6(Si6O18)(BO3)3(OH)4 R 3m 3m

Strunz Class:

VIII/E.19-30 VIII - Silicates

VIII/E - Cyklosilicates, six rings [Si6O18]12-

VIII/E.19 - Tourmaline group

VIII/E.19-05 Rossmanite! []LiAl2Al6(Si6O18)(BO3)3(OH)4 R 3m 3m

VIII/E.19-10 Elbaite Na(Li,Al)3Al6(BO3)3Si6O18(OH)4 R 3m 3m

VIII/E.19-15 Magnesiofoitite! [](Mg2Al)Al6(Si6O18)(BO3)3(OH)4 R 3m 3m

VIII/E.19-20 Dravite NaMg3Al6(BO3)3Si6O18(OH)4 R 3m 3m

VIII/E.19-30 Chromdravite NaMg3(Cr,Fe)6(BO3)3Si6O18(OH)4 R 3m 3m

VIII/E.19-35 Vanadiumdravite! NaMg3V6(Si6O18)(BO3)3(OH)4 R 3m 3m

VIII/E.19-50 Schorl NaFe3Al6(BO3)3Si6O18(OH)4 R 3m 3m

VIII/E.19-55 Foitite! []Na<0.5(Fe,Al)3Al6Si6O18(BO3)3(OH)4 R 3m 3m

VIII/E.19-60 Olenite! NaAl3Al6(BO3)3(Si6O18)(O,OH)4 R 3m 3m

VIII/E.19-70 Buergerite! NaFe3Al6(BO3)3Si6O21F R 3m 3m

VIII/E.19-75 Povondraite! (Na,K)(Fe,Fe)3(Fe,Mg,Al)6(BO3)3Si6O18(OH)4 R 3m 3m

VIII/E.19-80 Liddicoatite! Ca(Li,Al)3Al6(BO3)3Si6O18(O,OH,F)4 R 3m 3m

VIII/E.19-90 Uvite (Ca,Na)(Mg,Fe)3Al5Mg(BO3)3Si6O18(OH,F)4 R 3m 3m

VIII/E.19-100 Feruvite! (Ca,Na)(Fe,Mg,Ti)3(Al,Mg,Fe)6(BO3)3Si6O18(OH)4 R 3m 3m

Other Chromdravite Information

References:

NAME( Dana8) PHYS. PROP.(Enc. of Minerals,2nd ed.,1990) OPTIC PROP.(Dana8)

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Chromdravite

NaMg3(Cr,Fe+++)6(BO3)3Si6O18(OH)4
Dana No: 61.3e.1.11 Strunz No: VIII/E.19-30
Locality:

Notes: