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Appendix A - Discrimination of Precious Stones

Appendix A - Discrimination of Precious Stones Page of 366 Appendix B General Remarks about Carat, Rati,& Thola Text size:minus plus Restore normal size   Mail page  Print this page
Appendix.                                 319
colours of which differ to a greater or less extent. This property of exhibiting two colours is called dichroism, and the stone possessing it is said to be dichroic.
The following is a list of the principal gems which shew twin colours when seen with the dichroiscope, as given by Prof. Church, but slightly modified :—
This instrument, which is so familiar to the physicist, the chemist, and the astronomer, is not often used by the gem-expert ; but Prof, Church shewed, many years ago, that it might be usefully employed in the examination of certain stones. Thus, many transparent zircons, when viewed through the spectroscope, exhibit a characteristic series of black absorption-bands ; whilst another set of bands is shewn by most almandine-garnets.
Appendix A - Discrimination of Precious Stones Page of 366 Appendix B General Remarks about Carat, Rati,& Thola
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Streeter: Precious Stones and Gems
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