Tag Archives: minerals

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

Gottlobite: The “Thank God” Mineral

Gottlobite

  • Literally translated from German the meaning is “Thank God”; it is named after its type locality, the hill Gottlob (573 m) near Friedrichroda, Thuringia, Germany
  • Known only since 1996
  • Formula: CaMg(VO4,AsO4)(OH)
  • Space group: P212121 (No. 19)
  • Crystal system: orthorhombic
  • Crystal class: 222
  • Lattice parameters: a = 7.501 Å, b = 9.010 Å, c = 5.941 Å, α = β =  γ = 90°

gottlobite

Picture: CC BY-SA 3.0 de – Thomas Witzkehttp://tw.strahlen.org/typloc/gottlobit.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).)

gottlobite

View along the c axis.

  • MgO6 octahedra (orange)
  • AsO4/VO4 tetrahedra (purple)
  • Ca (blue)
  • Oxygen (red)

For a 3D interactive version, see here:

https://skfb.ly/6nBSF

Freieslebenite

Freieslebenite

  • Named after the mine commissioner of Saxony (Germany) Johann Carl Freiesleben
  • Formula: AgPbSbS3
  • Space group: P21/a (No. 14)
  • Crystal system: monoclinic
  • Crystal class: 2/m
  • Lattice parameters: a = 7.518 Å, b = 12.809 Å, c = 5.940 Å, α = 90°, β = 92.25°, γ = 90°

freieslebenite-169965

Picture: Rob Lavinsky, iRocks.com – 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).)

freieslebenite

View along the c axis.

  • AgS3 (ditorted) trigonal-planar coordination environment (gray)
  • SbS3 trigonal-pyramidal coordination environment (green)
  • PbS6 distorted octahedra (orange)

Dioptase: emerald-green and visible cleavage planes

Dioptase

  • The name dioptase comes from the Greek words “dia” (= through) and “optos” (= visible), alluding to the visible cleavage planes inside the often highly transparent or translucent crystals
  • Formula: CuSiO3 · H2O
  • Space group: R-3 (No. 148)
  • Crystal system: trigonal
  • Crystal class: -3
  • Lattice parameters: a = b = 14.566 Å, c = 7.778 Å, αβ = 90°, γ = 120°

Dioptase Tsumeb

Dioptase Tsumeb

Picture: Didier Descouens – 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).)

dioptase

View along the c axis.

  • six SiO4 tetrahedra (orange) are corner-connected to build a ring, so the mineral belongs to the cyclo silicates
  • the copper atoms (blue) are octahedrally coordinated by six oxygen atoms (red), four of them are oxygens involved in SiO4 tetrahedra and they occupy the equatorial positions of the CuO6 octahedra and two of them are oxygen atoms of water molecules, which occupy the axial positions of the CuO6 octahedra
  • the CuO6 octahedra are edge-connected and build a continuous 3D net

Orange-Red like Saffron: Crocoite

Crocoite

  • The name crocoite comes from the Greek “krokos” = saffron, alluding to the saffron-orange color of its powder
  • Formula: PbCrO4
  • Space group: P21/n (No. 14)
  • Crystal system: monoclinic
  • Crystal class: 2/m
  • Lattice parameters: a = 7.127 Å, b = 7.438 Å, c = 6.799 Å, α = 90°, β = 102.43°, γ = 90°

crocoite-360746_pd

Picture: Juergen Merzhttp://www.mindat.org/photo-360746.html
(This image has been released to the public domain.)


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).)

crocoite

View along the a axis.

Gray: Pb, red: O, orange: CrO4 tetrahedra

Cinnabar: Red as dragon blood and optically active

Cinnabar

  • probably named after the Persian word for dragon blood because of its characteristic red colour
  • used since ancient times as a pigment
  • Formula: HgS
  • Space group: P3121 (No. 152) or P3221 (No. 154)
  • Crystal system: trigonal
  • Crystal class: 32
  • Lattice parameters: a = b = 4.1347(6) Å, c = 9.4451(3) Å, αβ = 90°, γ = 120°

Modified by CombineZP

Modified by CombineZP

Picture: JJ Harrison (jjharrison89@facebook.com) – 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).)

cinnabar_01

View along the c axis.

cinnabar_02

View along the a axis.

  • the crystals structure is characteristic of chains with alternating sulfur and mercury atoms, which form helices with the helix axis running parallel to the c axis.
  • These helices are also the reason why crystals of cinnarbar are optically active (see: A.M. Glazer, K. Stadnicka, “On the origin of optical activity in crystal structures”. J. Appl. Cryst. 19 (2), 1986, 108–122. doi:10.1107/S0021889886089823

Bornite: Why order sometimes means less symmetry

Bornite

  • named after the Austrian mineralogist Ignaz von Born
  • also known as peacock ore because in air this mineral forms very quickly an iridescent coverage on its surface
  • Formula: Cu5FeS4
  • Space group: Pbca (No. 61)
  • Crystal system: orthorhombic
  • Crystal class: mmm
  • Lattice parameters: a = 10.950 Å, b = 21.862 Å, c = 10.950, αβγ = 90°

bornite_irocks

Picture: Rob Lavinsky, iRocks.com – CC BY-SA 3.0


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

bornite

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

  • yellow: Sulfur, blue: Copper, orange: Iron
  • The structure is based on a cubic-closest packing of sulfide ions; the copper and iron ions are located in 3/4 of the tetrahedral voids of the packing. At temperatures above 228 °C the cations are completely randomly distributed over these sites (the crystallographer names it disorder), forming a genuine (isometric) cubic phase, but in the low temperature modification the cations are more ordered, which is accompanied with the symmetry reduction to the orthorhombic crystal system