Tilasite Mineral Data

Tilasite Mineral Data +

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General Tilasite Information

Chemical Formula:

CaMg(AsO4)F

Composition:

Molecular Weight = 222.30 gm

Calcium 18.03 % Ca 25.23 % CaO

Magnesium 10.93 % Mg 18.13 % MgO

Arsenic 33.70 % As 51.70 % As₂O₅

Oxygen 28.79 % O

Fluorine 8.55 % F 8.55 % F

- % F -3.60 % -O=F₂

______ ______

100.00 % 100.00 % = TOTAL OXIDE

Empirical Formula:

CaMg(AsO₄)F

IMA Status:

Valid Species (Pre-IMA) 1895

Locality:

Langan, Varmland, Sweden. Link to MinDat.org Location Data.

Name Origin:

Named for Daniel Tilas (1712-1772), Swedish mining engineer.

Synonym:

ICSD 75618

PDF 2-485

Tilasite Image

Images:

Tilasite

Comments: Brownish, prismatic crystals of tilasite.
Location: Cervandone, Val d'Ossola Lombardy, Italy. Scale: Not Given.
© Lou Perloff / Photo Atlas of Minerals

Tilasite Crystallography

Axial Ratios:

a:b:c =0.8438:1:0.7486

Cell Dimensions:

a = 7.553, b = 8.951, c = 6.701, Z = 4; beta = 120.967° V = 388.46 Den(Calc)= 3.80

Crystal System:

Monoclinic - PrismaticH-M Symbol (2/m) Space Group: C 2/c

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

By Intensity(I/I_o): 3.246(1), 2.682(0.9), 3.073(0.8),

Forms:

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Forms: [ 0 1 0] [ 1 3 1] [ 1 1 1] [ 1 0 0] [ 0 0 1]

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Crystal Structure:

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Bladh K W , Corbett R K , McLean W J , Laughon R B , American Mineralogist , 57 (1972) p.1880-1884, The crystal structure of tilasite

Physical Properties of Tilasite

Cleavage:

[101] Good

Color:

Violet gray, Green, Gray, Pink brown.

Density:

3.77

Diaphaniety:

Translucent

Fracture:

Brittle - Generally displayed by glasses and most non-metallic minerals.

Habit:

Massive - Uniformly indistinguishable crystals forming large masses.

Habit:

Prismatic - Crystals Shaped like Slender Prisms (e.g. tourmaline).

Hardness:

5 - Apatite

Luminescence:

Fluorescent.

Luster:

Vitreous - Resinous

Optical Properties of Tilasite

Gladstone-Dale:

CI meas= 0.013 (Superior) - where the CI = (1-KPDmeas/KC)
CI calc= 0.021 (Excellent) - where the CI = (1-KPDcalc/KC)
KPDcalc= 0.1732,KPDmeas= 0.1746,KC= 0.177

Optical Data:

Biaxial (-), a=1.64, b=1.66, g=1.675, bire=0.0350, 2V(Calc)=80, 2V(Meas)=82.733. Dispersion r < v.

Pleochroism (x):

colorless.

Pleochroism (y):

colorless.

Pleochroism (z):

colorless.

Calculated Properties of Tilasite

Electron Density:

r_electron=3.60 gm/cc
note: r_Tilasite=3.77 gm/cc.

Fermion Index

Fermion Index = 0.01131
Boson Index = 0.98869

Photoelectric:

PE_Tilasite= 25.48 barns/electron
U=PE_Tilasite x r_electron= 91.61 barns/cc.

Radioactivity:

GRapi = 0 (Gamma Ray American Petroleum Institute Units)

Tilasite is Not Radioactive

Tilasite Classification

Dana Class:

41.5.6.1 (41)Anhydrous Phosphates, etc. Containing Hydroxyl or Halogen

(41.5)where (A B)2 (XO4) Zq

(41.5.6)Tilasite Group

41.5.6.1 Tilasite CaMg(AsO4)F C 2/c 2/m

41.5.6.2 Isokite CaMg(PO4)F C 2/c 2/m

41.5.6.3 Panasqueiraite CaMg(PO4)(OH,F) C 2/c 2/m

Strunz Class:

VII/B.25-30 VII - Phosphates, Arsenates and Vanadates

VII/B - Waterfree phosphates with unfamiliar anions F, Cl, O, OH. cations of medium and big size: Mg, Cu, Zn, and Ca, Na, K, Ba, Pb

VII/B.25 - Isokite - Thadeuite series

VII/B.25-10 Isokite CaMg(PO4)F C 2/c 2/m

VII/B.25-20 Panasqueiraite CaMg(PO4)(OH,F) C 2/c 2/m

VII/B.25-30 Tilasite CaMg(AsO4)F C 2/c 2/m

VII/B.25-40 Lacroixite NaAl(PO4)F C 2/c 2/m

VII/B.25-50 Durangite NaAl(AsO4)F C 2/c 2/m

VII/B.25-55 Maxwellite NaFe(AsO4)F Aa,A2/a Mono

VII/B.25-60 Nacaphite Na(Na,Ca)2(PO4)F P1 1

VII/B.25-70 Spodiosite? Ca2(PO4)F Pbcm 2/m 2/m 2/m

VII/B.25-80 Thadeuite (Ca,Mn)(Mg,Fe,Mn)3(PO4)2(OH,F)2 C 222₁ 2 2 2

Other Tilasite Information

References:

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

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Tilasite

CaMg(AsO4)F
Dana No: 41.5.6.1 Strunz No: VII/B.25-30
Locality:

Notes: