 Ametrine Quartz under crossed polars. The amethyst side shows classic Brazil law twinning. Photo: E. Skalwold |
 Strain halos around birefringent crystals in a Malaya garnet. Photo: E. Skalwold |
 Biaxial Optic Figure in Elbaite Tourmaline. Photo: E. Skalwold Although tourmaline is a uniaxial, there can be localized domains of lower symmetry which will manifest a biaxial optic figure. Such anomalous optical properties have been described in many gems including jeremjevite, apatite, quartz, garnet and diamond. Usually noted as "strain," they are caused by changes in chemical composition and/or changes during crystal growth. These fascinating effects are readily explored under the microscope using crossed polars. |
 Twinned calcite (see results here). Photo: E. Skalwold |
 Seeing Double Single-crystal rhodochrosite with two-phase inclusions and extreme doubling. Photo: E. Skalwold |
 The same scene through a polarizing filter which eliminates the doubling. Photo: E. Skalwold |
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