Aluminium

You might say it was hidden in plain sight. Aluminium is a highly reactive metal, meaning it readily undergoes chemical reactions with other elements and compounds to form different substances. As a result, nearly all of the naturally occurring aluminium atoms on Earth ended up tucked away in the molecules of more than 270 different minerals, including gemstones like emeralds and rubies. While it’s actually 8.2 per cent of the Earth’s crust, making it the most common metal and third-most common element, behind oxygen and silicon, you would never know it’s there without investigating on a chemical level.

The search was on