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

The impurities are what give gemstones their different colors.

Gems have crystalline structures, meaning the atoms appear in a regular, 3D pattern. For instance, aluminum oxide is made of aluminum and oxygen. But if you replace a tiny fraction (around 1% or less) of the aluminum with something else – like iron, titanium, vanadium, chromium, or various other metals – you can get different colors.

In the periodic table, these transition metals produce colors when they oxidize (chemical name for “rust”). You already know that iron becomes orange when it oxidizes. Chromium can be yellow or purple. Titanium can be pink or blue. Chromium can be red. And so on…

Different combinations of metals in different concentrations create a wide variety of colors in these crystals.