Monthly Archives: December 2019

Cassiterite – a Tin and Tantalum Source

Cassiterite

  • The name derives from the Greek kassiteros for tin
  • Cassiterite has been the chief tin ore throughout ancient history and remains the most important source of tin today
  • As often some of the tin atoms are substituted with iron, titanium, zirconium or tantalum, cassiterite, or to be precise, the smelting slag of SnO2, is in particular, also a source for tantalum
  • Belongs to the Rutile mineral group
  • Formula: SnO2
  • Space group: P42/mnm (No. 136)
  • Crystal system: tetragonal
  • Crystal class: 4/mmm
  • Lattice parameters: a = b = 4.7382(4) Å, c = 3.1871(1), αβγ = 90°

Picture: CarlesMillan – CC BY-SA 3.0


Crystal structure (click on the picture to download the VESTA file):

(K. Momma and F. Izumi, “VESTA 3 for three-dimensional visualization of crystal, volumetric and morphology data,” J. Appl. Crystallogr., 44, 1272-1276 (2011).)

  • SnO6 octahedra (slightly distorted) (purple)
  • Oxygen (red)

For a 3D interactive version, see also here:

https://skfb.ly/6PzLY

Ref.:

Structural Studies of Rutile-Type Metal Dioxides
A. A. Bolzan, C. Fong, B. J. Kennedy and C. J. Howard
Acta Cryst. B 1997, 53, 373-380
https://doi.org/10.1107/S0108768197001468

 

Ice V and XIII

Ice V and XIII

  • can be formed by slowly cooling liquid water at ~ 5 kbar from 20 °C to – 20 °C
  • density: 1.23 g/cm3

Structural features

  • Ice V is a proton-disordered phase
  • the analogous proton-ordered phase is Ice XIII
  • all water molecules are hydrogen-bonded to four others, two as donor and two as acceptor, at distances of 2.76 to 2.87 Å
  • the coordination tetrahedra are largely distorted with angles ranging from 84 to 128°.
  • Ice V contains 4,- 5-, 6-, and 7-membered rings
  • Space group: A2/a (No. 15)
  • Crystal system: monoclinic
  • Lattice parameters:
    • a = 9.22(2) Å, b = 7.54(1) Å, c = 10.35(2) Å
    • α = γ = 90°, β =109.2(2)°
    • 28 molecules per unit cell

 Here, you can download the CIF.

Literature:

[1] B. Kamb, A. Prakash, C. Knobler, Structure of Ice V, Acta Cryst. 1967, 22, 706-715. DOI: 10.1107/S0365110X67001409

Atomistic structure figures were created with

VESTA
K. Momma and F. Izumi, “VESTA 3 for three-dimensional visualization of crystal, volumetric and morphology data,” J. Appl. Crystallogr., 44, 1272-1276 (2011).