 Photo: E. Skalwold Twinned calcite (see results here). |
 Photo: E. Skalwold Strain halos around birefringent crystals in a Malaya garnet. |
 Photo: E. Skalwold Biaxial Optic Figure in Elbaite Tourmaline. 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. |
 Photo: E. Skalwold Ametrine Quartz under crossed polars. See Brazil law twinning 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. |
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