Rocks retrieved from a mine in Muzo, Colombia, show some of what makes the country the biggest producer of high-value emeralds. During a recent tour, geologist Camilo Pinzón uses a pickaxe to open a vein of white calcite rock that's streaked with green — the telltale sign of emeralds. This area was first mined by Indigenous groups long before the Spanish Conquest, yet it keeps yielding emeralds