Twinned Calcite.

Photo: E. Skalwold

Twinned calcite (see results here).



Malaya Garnet.

Photo: E. Skalwold

Strain halos around birefringent crystals in a Malaya garnet.



Biaxial Optic figure in Tourmaline.

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.




Ametrine Quartz.

Photo: E. Skalwold

Ametrine Quartz under crossed polars.
See Brazil law twinning here.




Extreme doubling in single-crystal rhodochrosite with two-phase inclusions.

Photo: E. Skalwold

Seeing Double
Single-crystal rhodochrosite with two-phase inclusions and extreme doubling.




Rhodochrosite with polarizing filter in place.

Photo: E. Skalwold

The same scene through a polarizing filter which eliminates the doubling.



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