A spectacular phenomenon that appears in the skies when the sun shines during a downpour, the rainbow has always fascinated by its beauty, its elusiveness and above all, its mystery. Literally forming a majestic bridge of light between earth and sky, it has inspired beliefs and religions across the world.

The link between Queen of Crime Agatha Christie and the world of beauty seems tenuous at first, but if you look at her beginnings as a novelist, it starts making sense. In 1966, she told the New York Times: "I got my plots in the tub, (…) just sitting there thinking, undisturbed, and lining the rim with apple cores." Hot baths did indeed bring her inspiration, the fruit of her imagination then scribbled in notebooks she scrupulously left in her bathroom and every room of her home, Greenway House, in Devon. The result? 66 crime novels, of which more than two billion copies were sold worldwide.

With 156 million entries on the net in a fraction of a second, stones and beauty are a good match. They’re now attending to our health and our well-being. To know them better and keep our heads cool, here is a short history of our beloved gems.