Author Archives: doktorholz

Celestial Celestine

Celestine

  • named from the Latin word caelestis meaning celestial, which in turn is derived from the Latin word caelum meaning sky or heaven because of its often soft blue color
  • pure Celestine is colourless
  • due to lattice defects in Celestine, colour centres are created which give the crystal its characteristic bluish colour
  • these centers are often additionally stabilized by the presence of pottasium ions
  • heating to over 200 °C “cures” these lattice defects and the mineral loses its color
  • radiation with X-rays creates new or more lattice defects and the color returns or can be intensified.
  • Formula: SrSO4
  • Space group: Pnma (No. 62)
  • Crystal system: orthorhombic
  • Crystal class: mmm
  • Lattice parameters:  a = 8.360 Å, b = 5.352 Å, c = 6.858 Å, αβγ = 90°

Picture: Rob Lavinsky, iRocks.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).)

  • SO4 tetrahedra (yellow)
  • SrO8 polyhedra (green)
  • Oxygen (red)

For a 3D interactive version, see here:

https://skfb.ly/6zG6R

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Porous materials, minerals and bees

Thoughtful and very well written. Nice analogy with the bees!

Molecular Dreams

Overwhelmed with the increasing flow of new scientific discoveries and related literature? You’re not alone. We live in the information overload era: too much to read, too little time, and life is short. Probably we’d need more readable, shorter papers too. Why writing a long one? Perhaps, it might connect disciplines which speak different languages but have much in common. Like material science and mineral science.

Let’s start from the first one.

You can make materials for solar cells, optical devices or medical sensors by trapping molecules or nanoparticles inside a “host”. Once there, molecules are no longer free to move, like in a gas or a liquid.  This process, called “confinement”, brings to life new properties, which were not present in the individual molecules and are very useful in technology.  Energy transfer or information storage, for instance, are made possible by the organization of the confined molecules

P1270522 The…

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Ice II (Ice-two)

Ice II (Ice two)

  • can be formed from hexagonal Ice (Ice Ih) at 198 K and 3000 bar or by decompressing Ice-five (Ice V) at 238 K
  • Ice II is likely to be a major rock-forming mineral in the outer Solar System
  • It may form a major proportion of icy moons such as Jupiter’s Ganymede
  • Density: 1.16 g/cm3

Structural features:

  • Ice-two is a proton-ordered form of ice
  • there are two types of 6-membered rings; one is almost flat (Type A) the other one has a more puckered, chair-like conformation (Type B)
  • these two types of rings are strictly alternating stacked along the c axis

  • If you look along the c axis, you will see that the two types of 6-rings are slightly rotated against each other (~ 16 degrees)

  • Space group R-3
  • Lattice parameters:
    • a = b = 12.935 Å, c = 6.233 Å
    • α = β = 90°γ = 120°

  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).]

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).]

Ice Ih

Ice Ih (Ice one hexagonal)

Structural features:

  • single molecule and molecular arrangement

  • Ice Ih is a proton-disordered phase

  • every water molecule is involved in 4 H-bonds (2 acceptors, 2 donors)
  • tetrahedrally coordinated
  • O-H bond length approx. 99 pm
  • H …. O-H distance approx. 175 pm
  • O … O distance approx. 275 pm
  • H-bond strength: approx. 21 kJ/mol
  • 6-membered rings
    • chair-like conformation in the (a,b) plane
    • boat-like conformation along the c direction

(graphic 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).

  • sometimes called “tridymite ice” because the oxygen atoms occupy the Si analogeous positions in the SiO2 phase tridymite
  • Space group P63/mmc
    • a = b = 4.4975 Å, c = 7.3224 Å
    • α = β = 90°, γ = 120°

 Here, you can download the CIF.

Eucryptite – not an altcoin but millionfold used in the kitchen

β-Eucryptite

  • Named from the Greek for “well” and “concealed”, in reference to its occurrence as intimate intergrowths with the mineral albite
  • It is the main component of the fameous glass-ceramic cooktops for stoves, known in the EU under the trademark Ceran® from Schott AG
  • Formula: LiAlSiO4
  • Space group: P6222 (No. 180)
  • Crystal system: hexagonal
  • Crystal class: 622
  • Lattice parameters: a = b = 10.500 Å, c = 11.194 Å, αβ = 90°, γ = 120°

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).)

  • SiO4 tetrahedra (orange)
  • AlOtetrahedra (light blue)
  • Li (purple/pink)
  • Oxygen (red)

For a 3D interactive version, see here:

https://skfb.ly/6wqY9