Antarcticite

Antarcticite

  • named after the type locality – the Don Juan Pond in Antarctica
  • Antarcticite is very hygroscopic and is formed only in very arid regions and precipitates only from highly saline brines
  • Formula: CaCl2  · 6 H2O
  • Space group: P321
  • Crystal system: trigonal
  • Crystal class: 32
  • Lattice parameters: a = b =  7.8759(2) Å, c = 3.9545(2) Å, α = β = 90°, γ  120°

Crystal structure (click on the pictures 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).)

  • every Ca ion is surrounded by nine water molecules
  • the CaO9 polyhedra (blue) are face-connected and stacked along the c axis
  • these faces are made up of three water molecules  acting as bridging ligands between two Ca ions
  • every Cl anion is involved in 6 H-bonds (dotted lines)
  • Oxygen (red)
  • Chlorine (green)
  • Hydrogen (white)

For a 3D interactive version, see here:

https://skfb.ly/6PJXV

Refs:

[1] T. Torii, J. Ossaka, Science 1965, 149, 975-977.
DOI: 10.1126/science.149.3687.975

[2] P. A. Agron, W. R. Busing, Acta Crystallogr. C 1986, 42, 141-143.
DOI: 10.1107/S0108270186097007

Troilite – most frequently from outer space

Troilite

  • Troilite occurs at only very few places on earth but  is abundant on our moon and also on Mars. The most frequent occurrences on earth are within meteorites.
  • Troilite was named after Domenico Troili who collected and examined samples of a meteorite that fell on earth in Albareto (near Parma) in 1766.
  • Formula: FeS
  • Troilite is the iron-rich endmember of the pyrrhotite group, the iron-deficient variant of FeS with the formula Fe(1-x)S (x = 0 to 0.2).
  • Space group: P-62(No. 190)
  • Crystal system: hexagonal
  • Crystal class: -6m2
  • Lattice parameters: a = b = 5.962(2) Å, c = 11.750(3) Å, α = β = 90°, γ = 120°

A section of the meteorite Sikhote Alin that has Troilite inclusions.

Picture: André Knöfel, CC BY-SA 3.0 de
https://commons.wikimedia.org/w/index.php?curid=7803661


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).)

  • Although it is a stoichiometric 1:1 compound the Fe (brown) and S (yellow) atoms do have different coordination environments:
    • FeS6 (distorted) octahedra
    • SFe6 (distorted) trigonal prisms
  • This is analogous to NiAs; however, in Troilite the unit cell represents a superstructure of the simple NiAs-type structure (P63/mmc) based on small displacements of the Fe and S atoms from their ideal positions leading to an overall reduced symmetry (P-62c).
  • The hexagonal close-packed sulfur framework remains essentially the same.

For a 3D interactive version on sketchfab, see here:

https://skfb.ly/6PHBS

Reference:
Lunar Troilite: Crystallography
H. T. Evans Jr
Science 1970, 167, 621-623

DOI: 10.1126/science.167.3918.621

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).

Vermiculite – Mineral of the Year 2019 in Austria

Vermiculite

  • The mineral was first described in 1824 by Thomas H. Webb. Due to the property of the mineral to expand into worm-like formations when heated to 200 to 300 °C in the direction of the crystallographic c-axis, Webb named it after the Latin word “vermiculor” for “worm breeder”.
  • On the occasion of the 195th anniversary of its discovery and due to its great importance as an industrial mineral, vermiculite was voted “Mineral of the Year” in Austria in 2019.
  • Formula: Mg0,7(Mg,Fe,Al)6(Si,Al)8O20(OH)4 · 8 H2O
  • Space group: C2/c (No. 15)
  • Crystal system: monoclinic
  • Crystal class: 2/m
  • Lattice parameters: a = 5.349 Å, b = 9.255 Å, c = 28.89, α = γ = 90°, β = 97.12°

Picture: CC BY-SA 3.0 Leon Hupperichs


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).)

For a 3D interactive version on sketchfab, see here:

https://skfb.ly/6OKvO

Tetrahedrite

Tetrahedrite

  • named after its common outer shape – a tetrahedron
  • because of its relative high copper content it is also a (minor) ore of copper
  • Formula: Cu12[S|(SbS3)4]
  • Space group: I-43m (No. 217)
  • Crystal system: cubic
  • Crystal class: -43m
  • Lattice parameters: a = bc = 10.448 Å, α = β = γ  = 90°

Picture: Carles Millan – http://www.mindat.org/photo-176605.html  | 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).)

  • SbS3 pyramids (purple)
  • CuS3 trigonal planar coordination (cyan)
  • CuStetrahedra (blue)
  • Copper (blue)
  • Sulfur (yellow)
  • Antimony (purple)

For a 3D interactive version on sketchfab, see here:

https://skfb.ly/6Or6R

Chemistry Hall

While travelling the US for 3 months (that’s the reason why this blog is currently silent 🙂 I received a message from the creators of a blog called Chemistry Hall.

This is a Blog that tries to make people understand how chemistry is important, and how to enjoy learning this incredible science.

This blog provides information in different forms: Research highlights, scientific outreach, educational resources, ways of learning chemistry, fun facts and curiosities, etc. They also love experimentation and share articles about home or hobby chemistry.

Have a look at:

https://chemistryhall.com/