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 = 102.65° 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.
Density: 3.5
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
Luminescence: Non-fluorescent.
Luster: Vitreous - Adamantine
Streak: gray

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
  ╔cole des Mines de Paris

Home Crystal X-Ray Chem Dana Strunz Determ A-Z Links