21. Eriochrome Black T has also been used to detect the presence of rare earth metals . 22. Pieces of rare earth metal which was discovered as an impurity in the mineral ytterbia. 23. All the discovered alkaline earth metals occur in nature. 24. The name " didymium " continued to be used in the rare earth metal industry. 25. The alkaline earth metals form difluorides that are insoluble. 26. In southern Ukraine, he found rare-earth metals beneath what would become the city of Samotkan. 27. Similar to yttrium, rare-earth metals from Gd to Lu can form REB 41 Si 1.2-type boride. 28. This reflected the belief at that time that thorium and the rare earth metals were divalent. 29. While most metals form arsenides, only the alkali and alkaline earth metals form mostly ionic arsenides. 30. The cathode is coated with oxides of alkaline earth metals , such as barium and strontium oxides.
