The chromium replaces about 1% of the aluminum in the corundum or beryl crystal when a ruby or emerald forms underground at a high temperature and pressure. But how can one element – chromium ...

Aluminum oxide (Al 2 O 3), also known as alumina, corundum, sapphire, or ruby, is one of the best insulators ... the structure deviates from that inside the crystal. The strongly insulating ...