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

Advertisement

Stibnite – a black make-up mineral

Stibnite

• Synonym: Antimonite
• The mineral has been known since ancient times and was used as a paste with fat as black make-up powder to color eyelids and eyebrows. In Arabic culture, dark eye rims are regarded as the ideal of beauty and at the same time as a magical repellent.
• Formula: Sb₂S₃
• Space group: Pnma (No. 62)
• Crystal system: orthorhombic
• Crystal class: mmm
• Lattice parameters: a = 11.3107 Å, b = 3.8363 Å, c = 11.2285 Å, α = β = γ = 90°

---

Picture: DerHexer, Wikimedia Commons, CC BY-SA 4.0

---

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).)

• SbS₅ tetragonal pyramids (purple)

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

https://skfb.ly/6JoCM

---

 

Abelsonite – a chemofossil

Abelsonite

• Discovered only in 1969 (by the way the year of birth of the author of this blog) by Lawrence C. Trudell while he was exploring the Green River Formation (Utah, USA) for an oil shale project
• Named after Philip H. Abelson (1913–2004), a long-time editor of the journal Science, for his pioneering work in organic geochemistry
• Abelsonite is formed as a secondary mineral (and is one of the few organic minerals)  on oil shale surfaces by conversion of chlorophyll – therefore, it is called a chemofossil (a fossil that consists only of chemicals remaining from the decomposition of a living organism)
• Abelsonite is the only known naturally occurring crystalline porphyrin derivative
• Formula: NiC₃₁H₃₄N₄
• Space group: P-1 (No. 2)
• Crystal system: triclinic
• Crystal class: -1
• Lattice parameters: a = 8.4416 Å, b = 10.8919 Å, c = 7.2749, α = 90.465°, β =113.158°,  γ = 78.080°

---

Picture: CC BY-SA 3.0 Thomas Witzke – http://tw.strahlen.org/fotoatlas1/abelsonite_foto.html

---

Crystal structure (click on the picture to download the CIF):

• Ni: green, N: blue, C: gray, H: white
• Note: Although a single Ni porphyrin molecule does not possess -1 symmetry, matching ethyl groups at roughly opposite ends of the molecule enable orientational disorder, in which molecules can randomly adopt one of two different orientations while still stacking in the same manner. The aggregate of these two random orientations produces an overall symmetry of P-1.
• Reference: Crystal structure of abelsonite, the only known crystalline geoporphyrin
  Daniel R. Hummer, Bruce C. Noll, Robert M. Hazen, Robert T. Downs
  American Mineralogist (2017) 102 (5): 1129-1132.
  https://doi.org/10.2138/am-2017-5927

Sartorite

• Named after Wolfgang Sartorius von Waltershausen (1809 – 1876) Professor of Mineralogy, University of Göttingen, Germany. He was the first who described the mineral.
• Formula: PbAs₂S₄
• Space group: P2₁/n (No. 14)
• Crystal system: monoclinic
• Crystal class: 2/m
• Lattice parameters: a = 19.62 Å, b = 7.89 Å, c = 4.19 Å, α = γ = 90°,  β = 90° (!)

---

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).)

• PbS₉ polyhedra (gray)
• AsS₃ trigonal pyramids (green)
• Sulfur (yellow)

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

https://skfb.ly/6IYWO