Their sparkle has mesmerised the world for generations. about one million years ago -long before the existence of life on earth as we know it – diamonds formed far beneath the surface, under the very special conditions of high pressure and relatively low temperatures.
75-100 miles above those diamonds was a surface covered with ocean, as the continents had not yet formed. There the diamonds sat for millions and millions of years, until they were thrust toward the surface by molten kimerlite a mere 55 million years ago. Rock and ash were blasted into the air in an explosive cloud, engulfing parts of redwood forest. The debris collapsed back into the ground and, once cooled, formed a conical “pipe”. Over the millions of intervening years, the remaining redwoods and the volcano tops were scraped away by erosion – the most recent of which was due to receding glaciers transporting bits of kimberlite miles away. The challenge for explorers was to trace those dislocated pieces (the indicators) back to the source.
Most diamonds are found in kimberlite, but not all kimberlite contains diamonds. Worldwide, there are roughly 5,000 known kimberlite deposits, but only 1% are considered to be worth mining.
For centuries, miners panned rives and stream beds, hoping to find diamonds. These gems were actually far from their original home, due to millions of years of erosion. Not until the 1800s did geologists discover kimberlite to be the diamond’s source.
Kimberlite, a dark, carbon-dioxide-rich rock, provides geologies a glimpse of what lies beneath. Embedded in it are a variety of heavy mineral calls indicators, which include distinctive olivine, garnets, and chrome diopside. Explorers use these minerals as “breadcrumbs” of sorts, following the indicator trail with the hopes of locating diamond-laden kimberlite pipe.