Erasmus Stephanus Jacobs was fifteen when he picked up the stone near the banks of the Orange River in 1867. What drew his eye is not recorded, but the 21.25-carat yellowish crystal must have caught the light differently from the surrounding gravel. Jacobs showed the stone to his neighbor, Schalk Van Niekerk, a man with enough curiosity about minerals to recognize something unusual. Van Niekerk passed it to John O'Reilly, a traveling trader, who carried it to Colesberg.

O'Reilly showed the stone around, but skepticism was the dominant response. South Africa was cattle country and sheep country, not diamond country. When Lorenzo Boyes, the acting Civil Commissioner, tested the stone by dragging it across a pane of glass, the scratch it left changed the calculus. Boyes sent it by post to Dr. William Guybon Atherstone, the foremost mineralogist in the Cape Colony, based in Grahamstown. Atherstone confirmed what the glass had suggested: this was a genuine diamond, and a fine one.

The Eureka Diamond, as it came to be called, was displayed at the 1867 Paris Exhibition, where it served notice to the world that southern Africa held mineral wealth worth pursuing. Within two years, prospectors were swarming the banks of the Orange and Vaal rivers, overturning gravel beds that had accumulated over millions of years. The discovery triggered what became known as the Diamond Rush, the event that launched South Africa's Mineral Revolution and transformed the region from a colonial backwater into one of the world's most contested territories.

The ripple effects were enormous. Kimberley sprang into existence as a mining camp and rapidly became one of the largest cities in the southern hemisphere. Cecil Rhodes built De Beers Consolidated Mines from the claims staked in those early years. The infrastructure demanded by mining, particularly railways, reshaped the physical and political geography of the subcontinent. Labor practices established in the diamond fields set patterns that would persist, with devastating consequences, through the gold rush and into the apartheid era.

The original rough stone weighed 21.25 carats. It was eventually cut into a 10.73-carat cushion-shaped brilliant, a reduction typical of early diamond cutting, where maximizing the stone's fire and clarity mattered more than preserving weight. The cutting diminished the stone's mass by half but revealed the warm, clear interior that Boyes had glimpsed when he scratched it against glass.

The Eureka changed hands several times over the following century, its value as a historical artifact growing as diamond mining reshaped the country it had been found in. In 1967, exactly one hundred years after Erasmus Jacobs picked it up from the riverbank, De Beers purchased the diamond and donated it to the people of South Africa. The company that owed its existence to the rush this stone had started returned it, symbolically at least, to the nation it had transformed. The Eureka was placed in the Kimberley Mine Museum, where it remains on display today.

The geology that placed a diamond in a boy's path near Hopetown is the same geology that studded the entire region with gems. Kimberlite pipes, formed between 120 and 90 million years ago, punched through the Earth's crust carrying diamonds from the upper mantle to the surface. Over tens of millions of years, erosion broke down the kimberlite and washed the diamonds into river gravels along the Orange and Vaal systems. These alluvial deposits accumulated in pockets and gravel terraces, concentrated by the same water action that sorts pebbles by weight.

Hopetown sits on the Orange River about 120 kilometers southwest of Kimberley. The landscape is arid and scrubby, classic Northern Cape terrain where the Karoo meets the river corridor. From the air, the Orange River traces a dark, winding line through pale earth. The alluvial terraces along its banks, where Jacobs found his stone, still yield diamonds today, though the easy pickings vanished more than a century ago.