Grimaldiite (α-CrOOH) Structure: ABC2_hR4_160_a_a_2a-002
| Prototype | CrHO$_{2}$ |
| AFLOW prototype label | ABC2_hR4_160_a_a_2a-002 |
| Mineral name | grimaldiite |
| ICSD | 64754 |
| Pearson symbol | hR4 |
| Space group number | 160 |
| Space group symbol | $R3m$ |
| AFLOW prototype command |
aflow --proto=ABC2_hR4_160_a_a_2a-002
--params=$a, \allowbreak c/a, \allowbreak x_{1}, \allowbreak x_{2}, \allowbreak x_{3}, \allowbreak x_{4}$ |
Other compounds with this structure
NaNiO$_{2}$
- CrOOH is found naturally in three forms. They are usually found together with Cr$_{2}$O$_{3}$ in a mineral known as merumite (Milton, 1976):
- Grimaldiite, rhombohedral $\alpha$–CrOOH (this structure),
- Guyanaite, orthorhombic $\beta$–CrOOH, and
- Bracewellite, orthorhombic $\gamma$–CrOOH is in the Lepidocrocite ($\gamma$–FeOOH, $E0_{4}$) structure.
- We use the $R3m$ data from Table IIIa (Christensen,1977), which locates the hydrogen atoms.
- Space group $R3m$ #160 does not specify the origin of the $z$-axis. Here we choose $z_{I} = 0$ for the position of the chromium atom.
- $\alpha$–CrOOH and CrCuS$_{2}$ have the AFLOW prototype label, ABC2_hR4_160_a_a_2a. They are generated by the same symmetry operations with different sets of parameters (
--params) specified in their corresponding CIF files. - Hexagonal settings of this structure can be obtained with the option
--hex.
\[ \begin{array}{ccc}
\mathbf{a_{1}}&=&\frac{1}{2}a \,\mathbf{\hat{x}}- \frac{\sqrt{3}}{6}a \,\mathbf{\hat{y}}+\frac{1}{3}c \,\mathbf{\hat{z}}\\\mathbf{a_{2}}&=&\frac{1}{\sqrt{3}}a \,\mathbf{\hat{y}}+\frac{1}{3}c \,\mathbf{\hat{z}}\\\mathbf{a_{3}}&=&- \frac{1}{2}a \,\mathbf{\hat{x}}- \frac{\sqrt{3}}{6}a \,\mathbf{\hat{y}}+\frac{1}{3}c \,\mathbf{\hat{z}}
\end{array}\]
Basis vectors
| Lattice coordinates | Cartesian coordinates | Wyckoff position | Atom type | |||
|---|---|---|---|---|---|---|
| $\mathbf{B_{1}}$ | = | $x_{1} \, \mathbf{a}_{1}+x_{1} \, \mathbf{a}_{2}+x_{1} \, \mathbf{a}_{3}$ | = | $c x_{1} \,\mathbf{\hat{z}}$ | (1a) | Cr I |
| $\mathbf{B_{2}}$ | = | $x_{2} \, \mathbf{a}_{1}+x_{2} \, \mathbf{a}_{2}+x_{2} \, \mathbf{a}_{3}$ | = | $c x_{2} \,\mathbf{\hat{z}}$ | (1a) | H I |
| $\mathbf{B_{3}}$ | = | $x_{3} \, \mathbf{a}_{1}+x_{3} \, \mathbf{a}_{2}+x_{3} \, \mathbf{a}_{3}$ | = | $c x_{3} \,\mathbf{\hat{z}}$ | (1a) | O I |
| $\mathbf{B_{4}}$ | = | $x_{4} \, \mathbf{a}_{1}+x_{4} \, \mathbf{a}_{2}+x_{4} \, \mathbf{a}_{3}$ | = | $c x_{4} \,\mathbf{\hat{z}}$ | (1a) | O II |
References
- A. N. Christensen, P. Hansen, and M. S. Lehmann, Isotope effects in the bonds of α-CrOOH and α-CrOOD, J. Solid State Chem. 21, 325–329 (1977), doi:10.1016/0022-4596(77)90130-X.
- C. Milton, D. E. Appleman, M. H. Appleman, E. C. T. Chao, F. Cuttitta, J. I. Dinnin, E. J. Dwornik, B. L. Ingram, and J. H. J. Rose, Merumite – A Complex Assemblage of Chromium Minerals from Guyanna (1976). Geological Survey Professional Paper 887.
Found in
- R. T. Downs and M. Hall-Wallace, The American Mineralogist Crystal Structure Database, Am. Mineral. 88, 247–250 (2003).
Prototype Generator
aflow --proto=ABC2_hR4_160_a_a_2a --params=$a,c/a,x_{1},x_{2},x_{3},x_{4}$