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Thortveitite Mineral Data

General Information
Chemical Formula:(Sc,Y)2Si2O7
Environment:Granitic pegmatite rocks.
Locality:Iveland, Setesdal, Norway.
Name Origin:Named after the Norwegian engineer, O. Thortveit.
Dana Class:55.2.1a.4 (55)Si2O7 Groups, Generally with No Additional Anions (55.2)with cations in [6] coordination (55.2.1a)Thortveitite group
Strunz Class:VIII/C.01-10 – Silicates [Sorosilicates, with [Si2O7]6-, without anions unfamiliar to tetraheders (Thortveitite – Rowlandite-(Y) series).]
Axial Ratios:a:b:c =0.7706:1:0.5493
Cell Dimensions:a = 6.587, b = 8.547, c = 4.695, Z = 2; beta = 102.65ø V = 257.91
Crystal System:Monoclinic – Prismatic H-M Symbol (2/m) Space Group: C2/m
X Ray Diffraction:By Intensity(I/Io): 3.11(1) 3.13(1) 2.93(0.45)
Physical Properties
Cleavage:[100] Perfect
Color:brown, grayish black, black, or grayish green.
Diaphaniety:Translucent to opaque
Habits:Crystalline – Fine – Occurs as well-formed fine sized crystals., Radial – Crystals radiate from a center without producing stellar forms (e.g. stibnite), Prismatic – Crystals Shaped l ike Slender Prisms (e.g. tourmaline).
Hardness:6.5 – Pyrite
Luster:Vitreous – Adamantine
Optical Properties
Optical Data:Biaxial (-), a=1.756, b=1.793, g=1.809, bire=0.0530, 2V(Calc)=64, 2V(Meas)=65.
Pleochroism (x):deep green.
Pleochroism (y):brownish yellow.
Pleochroism (z):brownish yellow.
Other Information
References:NAME( Duda&Rejl90) PHYS. PROP.(Enc. of Minerals,2nd ed.,1990) OPTIC PROP.(Ford32)
See Also: Athena Mineralogy
 Frederic Biret
 École des Mines de Paris

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