Hi Jacob,
Chek out Section 2 in the following paper:
Echalier et al. (2004) Assessing crystallization droplets uding
birefringence.
Acta Cryst D60, 696-702.
It offers a very effective summary of the physical basis of crystal
birefringence and reiterates the classification of crystal optics based
on isotropic, uniaxial and biaxial systems. My understanding is that a
favorable crystal orientation with respect to the direction of view is
important for being able to observe appreciable birefringence from
uniaxial and biaxial crystals. This can be especially tricky to get from
biaxial crystals, i.e. crystals with orthorhombic or monoclinic or
triclinic point-group symmetry, projecting their optically anisotropic
axis in the plane of the view. Crystals with cubic symmetry are
optically isotropic and are therefore not birefringent.
Best wishes
Savvas
-----Original Message-----
From: CCP4 bulletin board [mailto:[log in to unmask]] On Behalf Of
Jacob Keller
Sent: Thursday, June 12, 2008 2:33 AM
To: [log in to unmask]
Subject: [ccp4bb] birefringent spacegroups
Dear Crystallographers,
is there a list somewhere of spacegroups which can and cannot be
birefringent? Upon what feature of the spacegroup does this depend?
Jacob Keller
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Jacob Pearson Keller
Northwestern University
Medical Scientist Training Program
Dallos Laboratory
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