undermine pearl the size of it of tennis nut feature in thePlanet Earth IIIepisode “ Extremes ” , which dives into Hang Son Doong Cave , a straggle limestone cave place in Phong Nha - Kẻ Bàng National Park in Vietnam . As one of the largest cave on Earth , it ’s a portal to a populace of quirk include animals hold out in zero light conditions , and unique geologic shaping . It ’s also a hot place for cave pearls .
Cave pearls , also fuck as oolites , are globular rock formations unique to limestone cave . This is because limestone caves are uniquely form by urine gnaw John Rock , and water plays a cardinal role in the geological formation of glossy cave pearls . A type of speleothem ( structures formed in cave by the deposition of minerals from pee ) , they ’re made up of layers of themineralscalcite or aragonite , both crystalline forms of Ca carbonate .
Just like regular pearls , the calcium carbonate layer are organized in concentrical layers because of the way of life a celestial sphere allows for the dandy amount of deposit on the small surface . They ’re also similarly glossy due to the impress H2O that keeps them dainty and still , but they can quickly cheapen once dry .
Their smooth , spherical pearliness is the result of the unique way in which they form from a small nucleus , which might be a single grain of sand or a mineral crystal . Over clip , that nucleus gets coated with layers of calcium carbonate that make out from mineral - rich water drop falling from the cave ceiling . The drops of water think the core group is constantly go , never quite affixing to the cave level and forming in a spherical cast interchangeable to pearls that develop insideoysters .
undermine pearl geological formation is a dense process that can take thousands of years , and bet on how long it ’s been , they can be tiny specks , or – as in the case of Hang Son Doong – elephantine pearls the size of it of tennis balls . While their oyster craftsman counterparts have been used in jewellery , cave pearls seem in fashion items less often , but there are some examples – such as this antiquecave pearl necklace .
The spherical formations come in in many colors , include lime green cave pearl that were name in Yemen ’s legendary “ Well of Hell ” . They were describe on what ’s thought to be the first - ever human expedition into the rude swallow hole , direct to the breakthrough of cave pearls , dead creature , and snakes .
Hang Son Doong do with its own unique challenge , accept thePlanet Earth IIIteam 200 metre ( 650 feet ) deep underground where they camped for 18 days , ready it the longest expedition ever into the sprawl limestone cave . Fancy taking a face around ? you could catchExtremes on BBC iPlayernow .
