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MINERALS AND SYNTHETIC COMPOUNDS, AmXn, IN WHICH X
ATOMS ARE |
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CLOSE PACKED AND A ATOMS OCCUPY OCTAHEDRAL INTERSTICES |
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Diaspore |
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click here to see a key to this data bar
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octa |
50% |
hcp |
3-d |
4
edges, 1 vertex |
A-
6c, X- 3c/hcp |
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structure |
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In the diaspore
structure X anions (O and OH) are packed HCP with metal ions
in |
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50% of the octahedral interstices of each
successive layer. Diaspore is similar to |
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rutile except that double chains of
AX6
groups of atoms comprise the structure. |
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Ex.
a-AlO.OH
(aluminum oxyhydroxide, diaspore ) ( Al - A ; O , OH - X ) |
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Crystal lattice |
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The doubled rows of
occupied AX6 groups in each layer are demonstrated to be |
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separated by doubled rows of unoccupied
octahedral voids. Like the rutile structure |
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these doubled rows are staggered relative to
each other in each successive layer so |
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that they are linked by their exposed vertices. |
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Figure 88 |
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click image |
Diaspore lattice |
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to
enlarge |
structure |
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Polyhedral framework |
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linking surfaces |
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Figure 89 - Diaspore |
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polyhedral framework |
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4
edges, 1 vertex |
click image to enlarge |
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The doubled chains are
clearly visible in the framework model as is their linkage. |
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The OH ions are located at the vertices of the
edges linking the AX6 groups together |
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into the double chains. The O atoms are
located at the vertices linking the doubled |
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chains of each successive layer to each other.
(the blue triangles are braces) |
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Cleavage |
Crystal habit |
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(100) - perfect, (110) - less so |
tabular - parallel
to (100) |
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Isostructural minerals/compounds |
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a-FeO.OH,
a-MnO.OH,
a-ScO.OH,
VO.OH |
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Page
58 - Structure matters - Diaspore |
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