sentence: Red corundum is called Ruby.
sentences_before: Sapphire is actually just corundum and is one of the hardest minerals on the hardness scale. The usual color that sapphire comes in is blue. Sometimes it comes in black, yellow, pink, purple, clear, green, orange, white, but it never comes in the color red.
concept_name: red corundum
headings: Sapphire
categories: Gemstones Birthstones