Abstract
Twinning process in aragonite and its isotypes on (110) may be described by OD (order -disorder) mechanism. In the Pmcn orientation of aragonite, the OD layer has layer group P(c)mb, with the direction perpendicular to the layer indicated by parentheses. The lattice parameters of the OD layer are b 9.39 Å (the [110] diagonal of the aragonite lattice) and c 5.74 Å, its thickness a is d(110) of the aragonite lattice, equal to 4. 21 Å. The interlayer σ-PO's are {(22/n1/2,1)2-1/2/a221/n2,-1/2}, brackets denote the direction perpendicular to the OD layer. Two polytypes with maximum degree of order can be derived. MDO1 is Pmcn aragonite itself, MDO2 is a Pcab polytype with a 8.42 Å, b 9.39 Å and c 5.74 Å, unknown as an independent structure. Desymmetrization of the aragonite structure appears to limit occurrence of the MDO2 principle to occasional twin boundaries.
| Original language | English |
|---|---|
| Journal | Mineralogy and Petrology |
| Volume | 106 |
| Issue number | 1-2 |
| Pages (from-to) | 19-24 |
| Number of pages | 6 |
| ISSN | 0930-0708 |
| DOIs | |
| Publication status | Published - Sept 2012 |