Antigorite: Antigorite is a serpentine-group mineral with transverse modulation. Polytypes of antigorite are commonly incommensurate, and require structure solution in 4-dimensions. Stacking defects, twinning, and modulation dislocations obscure the structure's solution with SC-XRD. In spite of these obstacles, the models using SC-XRD data and 4D solution are likely accurate, with stacking defects and twinning accounting for a large portion of the R1 discrepancy. Most significant to geologists is antigorite's apparent structural sensitivity to chemical and geologic environment, where modulation wavelength reflects serpentinization temperature. This may in part be due to site occupancies (occupancies across the modulation) of Al and Fe along with the abundance of H, which propagate the incommensurate perturbations in the structure. Below are examples of a 3D and 4D solution of two different polytypes of antigorite.
19cs001a_2_0m_a.cif | |
File Size: | 3916 kb |
File Type: | cif |
grangeantbig_0m.cif | |
File Size: | 412 kb |
File Type: | cif |
Some example single crystal x-ray diffraction files (CIF, INS, and HKL).
Pyroxenes
Monoclinic:
C2/c
dh203_0m.cif | |
File Size: | 238 kb |
File Type: | cif |
dh203_0m.hkl | |
File Size: | 225 kb |
File Type: | hkl |
dh203_0m.ins | |
File Size: | 3 kb |
File Type: | ins |