America’s only rare-earths mine suspended operations this week amid the bankruptcy of its owner, Colorado-based Molycorp Inc. Does this mean China is succeeding in controlling the world market for strategic minerals used in missiles, smartphones, electric cars and other high-tech products? Far from it.

Much has changed since Beijing sparked a rare-earths panic in 2010. China was home to 95% of the world’s production, so when it tightened export quotas by 40% and then cut off shipments to Japan over a territorial dispute, buyers...