ʻO Ruby [1] , ʻo ia hoʻi ka corundum o ka waihoʻoluʻu ʻulaʻula, he ʻano corundum a ʻo ia ka mea nui o ka alumini oxide (AL 2O 3).ʻO ke kala ʻulaʻula mai ka chromium (CR), ka nui o Cr2O3, ʻo ka ʻike maʻamau he 0.1 ~ 3%, ʻo ka mea kiʻekiʻe loa he 4%.Loaʻa i ka Fe, Ti a me ka uliuli i ʻōlelo ʻia ʻo Sapphire, non-chromium CR kala o nā kala ʻē aʻe o ka corundum i ʻike pū ʻia ʻo Sapphire.