Tag Archives: crystal structures

Afwillite – a calcium nesosilicate

Afwillite

  • Named after the abbreviated discoverer Alpheus Fuller Williams (1874–1953), CEO of De Beers Consolidated Mines at that time
  • Formula: Ca3(SiO3OH)2 · 2 H2O
  • It belongs to the nesosilicates, i.e. there are only isolated SiO4 tetrahedra
  • Space group: Cc (No. 9)
  • Crystal system: monoclinic
  • Crystal class: m
  • Lattice parameters: a = 16.278 Å, b = 5.6321 Å, c = 13.236, α =  γ = 90°, β = 134.898°

Picture: Matteo Chinellato – http://www.mindat.org/photo-356015.html | CC BY-SA 3.0


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).)

  • Oxygen (red)
  • Hydrogen (white)
  • SiO4 tetrahedra (yellow)
  • CaO7 polyhedra (light blue)

For a 3D interactive version, see here:

https://skfb.ly/6J7oy

Advertisements

Strengite

Strengite

  • Named after Johann August Streng (1830-1897), German mineralogist, University of Giessen, Germany
  • Formula: FePO4 · 2 H2O
  • Space group: Pbca (No. 61)
  • Crystal system: orthorhombic
  • Crystal class: mmm
  • Lattice parameters: a = 8.722 Å, = 9.878 Å, c = 10.8117 Å, αβ = γ = 90°

Picture: Christian Rewitzer  | 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).)

  • FeO6 octahedra (dark-red)
  • POtetrahedra (green-blue)
  • Oxygen (red)
  • Hydrogen (white)

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

https://skfb.ly/6BVJs

Ice Ic

Ice Ic ( Ice one cubic)

  • can be formed by condensation of water vapour at reduced pressure well below -80 °C
  • is metastable with respect to Ice Ih (approx. + 50 J/mol)
  • it seems to be very difficult to grow large phase-pure Ic ice crystals; they contain, to a certain extent stacking-disordered or hexagonal ice

Structural features:

  • like hexagonal ice cubic ice is a proton-disordered phase
  • every water molecule is involved in 4 H-bonds (2 acceptors, 2 donors)
  • tetrahedrally coordinated
  • O-D bond length approx. 101 pm
  • D …. O-D distance approx. 174 pm
  • O … O distance approx. 275 pm
  • 6-membered rings (exclusively chair conformation)

  • sometimes also called “cristobalite ice” because the oxygen atoms occupy the Si analogeous positions in the SiO2 phase cristobalite
  • it would be also justified to call it diamond-like ice 🙂
  • Space group Fd-3m
    • a = b = c = 6.3510 Å
    • α = β = γ = 90°

 

  Here, you can download the CIF.

[Atomic structure figures 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).]

Samsonite

Samsonite

  • Named after its type locality, the Samson Vein of Andreasberg silver mines, Harz Mountains, Germany.
  • Formula: Ag4MnSb2S6
  • Space group: P21/(No. 14)
  • Crystal system: monoclinic
  • Crystal class: 2/m
  • Lattice parameters: a = 10.3861 Å, b = 8.1108 Å, c = 6.6630 Å, α = γ = 90°, β = 92.639°

 


Picture: Christian Rewitzer  | 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).)

  • MnO6 octahedra (purple)
  • SbS3 trigonal pyramids (blue)
  • AgSdistorted tetrahedra (gray)
  • AgStrigonal-planar coordination (green)
  • Sulfur (yellow)

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

https://skfb.ly/69Hqz

Rodalquilarite

Rodalquilarite

  • Named after its type locality, the Rodalquilar gold deposit, Almeria, Spain
  • Formula: Fe2(TeO2OH)3(TeO3)Cl
  • Space group: P-1 (No. 2)
  • Crystal system: triclinic
  • Crystal class: -1
  • Lattice parameters: a = 5.103 Å, b = 6.653 Å, c = 9.012 Å, α = 73.40, β = 78.03° γ  = 76.76°

Picture: Christian Rewitzer  | 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).)

 

  • FeO6 octahedra (brown)
  • TeO3 trigonal pyramids (blue)
  • Oxygen (red)
  • Hydrogen (white)
  • Chlorine (green)

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

https://skfb.ly/69DIu

Jarosite – Indicator of (liquid) water on Mars

Jarosite

  • Named after its type locality, Barranco del Jaroso in the Sierra Almagrera (near Los Lobos, Cuevas del Almanzora, Almería, Spain)
  • In 2004 the Mars Exploration Rover – B found Jarosite on Mars. Because on Earth Jarosite is only formed in liquid water, this finding strongly indicates that Mars once possessed large amounts of liquid water.
  • Formula: KFe3(OH)6(SO4)2
  • Space group: R-3m (No. 166)
  • Crystal system: trigonal
  • Crystal class: -3m
  • Lattice parameters: a = b = 7.304 Å, c = 17.268 Å, αβ = 90°, γ = 120°

Picture: CC BY-SA 3.0 | Christian Rewitzer


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).)

  • KO12 only very slightly distorted icosahedra (purple)
  • FeO6 octahedra (blue)
  • SO4 tetrahedra (yellow)
  • Oxygen (red)

For a 3D interactive version, see here:

https://skfb.ly/6pGuY

Hercynite – A ferro spinel

Hercynite

  • Named after the latin name Silva Hercynia of the Bohemian Forest, where this mineral was first found
  • it is a ferro spinel
  • Formula: FeAl2O4
  • Space group: Fd-3m (No. 227)
  • Crystal system: cubic
  • Crystal class: m-3m
  • Lattice parameters: a = b = c = 8.1458 Å, α = β =  γ = 90°

Picture: CC BY-SA 3.0 nl | Fred Kruijen | http://www.mindat.org/photo-73060.html

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).)

  • FeO4 tetrahedra (orange)
  • Al (blue), octahedral oxide coordination environment
  • Oxygen (red)

For a 3D interactive version, see here:

https://skfb.ly/66QEE