Babbage from The Economist (subscriber edition) Critical chemistry: what makes rare earths so special?
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Sep 24, 2025 
Andrea Sella, a Professor of chemistry at University College London and an expert on rare-earth elements, discusses the unique electronic and magnetic properties of lanthanides. Tim Cross, The Economist's senior science writer, tackles the pressing geopolitical implications surrounding rare earths, especially China’s export controls. They explore the critical roles these elements play in technology, the challenges of recycling, and potential alternatives for Western industries. Could this be the wake-up call for a shift in global supply strategies?
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Lanthanides’ Hidden Electrons Explain Their Magic
- The lanthanides (rare earths) are a block of 14 elements with very similar chemistry but distinct electronic characters.
- Their shared 3+ ionic state and buried 4f electrons make their outer chemistry uniform while giving unique magnetic and spectral traits.
Buried 4f Electrons Make Their Chemistry Uniform
- The rare earths' 4f electrons are contracted and buried close to the nucleus due to quantum mechanics.
- That contraction makes their ions behave like little spheres externally while their inner electrons drive unique optical and magnetic properties.
Sparking Mish Metal Demonstration
- Andrea Sella demonstrated mish metal sparking when struck and explained early uses for lighting fires.
- The brittle lanthanide-iron alloy produces tiny reactive fragments that ignite in air, giving bright white sparks.