"Alexandrite" is a crystalline semi-precious stone which is normally yellowish in daylight.
The "czars' lost jewels" in the flavor text may refer to the Russian Crown Jewels which were last used to crown Czar Nicolas II and his wife, Empress Alexandra. The jewels went missing for a time after the USSR used them as collateral for a loan from Ireland, which was subsequently thrown into its own revolution.
Alexander and its variants (Alexei, Alexandra, etc.) were common names in the Russian monarchy.