Most islands are built by volcanoes or coral. Zabargad is neither. When the African and Arabian plates pulled apart to open the Red Sea, they cracked the crust so violently that a slab of the upper mantle, the layer that normally sits tens of kilometers below your feet, was wrenched upward and exposed. Geologists travel here to walk across rock they otherwise study only as fragments carried up by eruptions. Three masses of a rock called peridotite form the island's bones, threaded with the olive-green crystals of olivine. The highest point rises 235 meters above water that is otherwise impossibly blue. Stand on the summit and you are standing on a fossil of the Earth's interior, hauled into the sunlight.

Gem-quality olivine is peridot, and Zabargad is its oldest known source. Mining here began around 300 BCE under the Ptolemaic pharaohs, and the stone reached Egyptian queens and Roman collectors. For centuries scholars doubted whether the ancient workings were real, until a 2010 geo-archaeological expedition confirmed them: old mine pits, ruined buildings, a water well, all evidence of work that continued for nearly eight hundred years. The miners learned to search at dusk, when the low light made the crystals easier to spot scattered in the pale rock. Pliny called peridot the evening gem and claimed the island was guarded by watchers ordered to kill trespassers, and that fogs so often shrouded it that sailors struggled to find it at all. The legend was likely a Ptolemaic trade secret, a way to keep a royal monopoly hidden behind fog and fear. The stone's pull never really faded; centuries later, gem dealers still spoke of Zabargad as the original home of the finest green olivine.

Above the water, almost nothing grows. There is no soil to speak of, only bare igneous rock, so plant life is sparse and stubborn. The island compensates below the surface. A ring of coral wraps Zabargad roughly 25 meters down, sheltering rays, moray eels, octopus, cuttlefish, and the well-camouflaged crocodilefish. Divers prize these reefs, though the same attention has cost them: tourism and the growth of the diving industry damaged the coral and disturbed nesting birds badly enough that the island was once closed to visitors for a full year. Now protected as part of Elba National Park, Zabargad shelters at least nine breeding bird species, including roughly 150 pairs of sooty falcons recorded here in October 1994. The contrast defines the place: a barren green stone above the waterline, and a crowded living reef just beneath it.

Zabargad sits just north of the Tropic of Cancer in Foul Bay, the largest of a small cluster of islands that includes the aptly named Rocky Island to the south. For most modern travelers it remains what it was for the Ptolemies: a hard place to reach, more rumor than destination. Liveaboard dive boats use it as a stop-off on the way to Rocky Island's deeper walls. The beaches stay quiet and largely undeveloped. It is a strange thing to realize, sunbathing on this lonely shore, that the sand beneath you is the cooled flesh of the planet, and that the green pebble in a museum case in Cairo or London may have been chipped from this very ground when the Pharaohs still ruled.