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Figure 7
Morphological details of the known polymorphs in 1,8-dihydroxyanthraquinone. The optical micrographs of the birefringence help to differentiate between the polymorphs. Polymorph 1, calculated with 20% polarity, is known to show strong anomalous birefringence in contrast to 5, which is almost perfectly extinct along the optic axis with a small reminiscence of {101} growth sectors. Polymorph 3 exhibits extinction at an angle close to 135° and the intrinsic birefringence is fairly strong. When looking along (001), the crystals are pseudo orthogonal at an angle of γ = 88.995 (11)°. No micrograph was available for polymorph 4. All samples were ca 1 mm across. Because of strong linear dichroism, the extinction angle shown for polymorph 2 appears 45° clockwise rotated. The phase factor δ = 2πΔnL/λ is related to the birefringence, Δn, wavelength of light, λ, and sample thickness, L. Further details of polarimetric methods used here are outlined elsewhere (Kaminsky et al., 2004BB16).

Journal logoJOURNAL OF
APPLIED
CRYSTALLOGRAPHY
ISSN: 1600-5767
Volume 40| Part 2| March 2007| Pages 382-385
doi:10.1107/S0021889807003986
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