Why are rubies red?

You’d be surprised to know that rubies get their beautiful red colour from impurities that are present in the gemstone. It’s intriguing how an impurity gives this gem it’s most defining property. Now, we could leave it at that or draw a life lesson from it. (We love drawing life lessons from things so here it is). Just like it is with the ruby, our impurities or imperfections make us who we are, they make us – us.

Now back to the science-y part of things. Rubies are a kind of crystal called corundum, which is a form of aluminum oxide. The presence of chromium in this crystal is what gives it its red colour. The chromium impurities absorb specific colors of light, only allowing red light to pass through the stone. The redness of the ruby depends on the amount of chromium present in it.

The amount of chromium in a corundum can also be altered. The ruby can be treated and its impurities removed, which leaves us with a clear crystal or more chromium can be added to it, thus increasing the intensity of its colour. The presence of different impurities and elements in the corundum gives the crystal different colours, for example, the presence of iron and titanium in a corundum creates a sapphire.

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