eli5 What determines whether a gem is a sapphire, ruby, emerald, diamond, etc if those gems don’t necessarily have to be the most common thought color? For example, sapphires can be colors other than blue. What’s the difference between a red sapphire and a ruby?

Question

eli5 What determines whether a gem is a sapphire, ruby, emerald, diamond, etc if those gems don’t necessarily have to be the most common thought color? For example, sapphires can be colors other than blue. What’s the difference between a red sapphire and a ruby?

In: 5800

Answer 1

Sapphire and ruby are both *corundum,* a crystal made of aluminum oxide, but with different colors due to trace amounts of various other chemicals. If it’s colored red, we call it ruby, otherwise we call it sapphire. There’s no difference between a red sapphire and a ruby (other than the name we give it).

Emerald is a totally different chemical compound, namely *beryl* or beryllium aluminium silicate, which can occur in its own range of colors depending on what trace elements it contains.

Diamond is yet another totally different chemical compound, made of pure carbon.