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Black stone beach
Anjouan island , off easterly seacoast of Africa , is mostly made of dark volcanic rocks , like these cobble on the shoreline of one of the island ’s beach . But investigator have now find a motherlode of " impossible " rocks on a ridge on the island . These out - of - place rocks are made of quartzite , a metamorphic rock-and-roll that forms from sandstone , as in a riverbed or delta — not a vent . [ translate more about the Anjouan island rocks ]
Out of place
Local boys resist near a hunk of quartzite on Anjouan island . The rock candy does n’t look like anything that could have formed on volcanic Anjouan , said Cornelia Class , a geochemist at the Lamont - Doherty Earth Observatory at Columbia University . Geologists have been get to scattered reports of quartzite on Anjouan for 10 . In September 2018 , Class led a field expedition to the island to find out how much quartzite there really is and where it ’s coming from .
Mountain of mystery
The motherlode of quartzite change by reversal out to be near this mountain village , called Tsembehou , which is nestled among heavily forested volcanic slope . A nearby ridgepole call Habakari N’gani is nearly half quartzite , Class and her colleagues found . This John Rock somehow end up in the middle of the ocean basin between Africa and Madagascar , which should n’t host any quartzite at all . Incredibly , as volcanic Anjouan take shape , the quartzite snarf up along with its volcanic Rock some 13,120 feet ( 4,000 cadence ) from the ocean bottom .
A use for quartzite
A local named Ali Saindou demonstrates how Anjouan resident use the cobbles of quartzite they get hold around the island . " We happen these all the meter when we ’re planting Manihot utilissima , " Saindoutold Columbia ’s Kevin Krajick . " mass apply them to focalise knife . "
Because multitude use the quartzite , much of it has been cleared out of streambeds and river where it erodes , Class told Live Science . That made hunting for the source of the modest boulder of quartzite even more thought-provoking .
On the hunt
Cornelia Class of the Lamont - Doherty Earth Observatory uses a rock hammer to break apart a sample on the side of a road in Anjouan . Researchers searched for quartzite in outcrops by the incline of route , in forest clearings and even in manmade rock walls , where scattered chunks of white sometimes peek out from boulders of volcanic basalt .
Quartzite, found
Cornelia Class holds a fresh discovered piece of quartzite as Comorian authorities scientist Bourhane Abderemane expect on . The researchers had old geological maps guiding them toward previously discovered quartzite rock outcrop , but earlier reports were scattered and fragmentary .
Heavy work
Comorian authorities geologist Hamidi Soulé prepare to crack into a roadside rock outcrop in search of quartzite . Anjouan island is a unmanageable place for a geologist , Class said , because most of the rocks on the island are covered with loggerheaded layers of filth and vegetation . excavate roadbeds are one plaza where break rocks can be find .
Uphill march
researcher bushwhack uphill while on the hunt for the source of the quartzite boulders regain dotting the hillside on Anjouan . " It ’s basically like a self-aggrandizing garden , " socio-economic class say of the island . The researchers combed the area systematically , map occurrences of quartzite and require local residents to point them to where they ’d determine the white Boulder .
Flying fruit bat
An tremendous yield squash racket wings its manner over the hatful of Anjouan . Livingstone ’s fruit bats ( Pteropus livingstonii ) are found only on Anjouan and a nearby island , Mohéli . The cricket bat can have wingspread of up to 4.5 feet ( 1.4 meter ) .
Clues in a cowfield
Hidden beneath the soil below this cow ’s feet is the motherlode : A large down payment of quartzite , make up near half of a lot . The quartzite social unit was much large than expected , Class pronounce . A span pocket-size glob of the rock that have weathered out from the primary consistence of quartzite are propped next to the moo-cow ’s front feet .
Ocean and land
A view from Anjouan overlook the sea . As the island was formed by a volcano , it should be entirely igneous , volcanic rock and roll . The presence of the quartzite – a metamorphous rock candy forge from sandstone originally laid down in a river delta or on a beach — is dumbfound . The rock likely follow from the African continent , Class said , but it ’s not absolved how it get into the middle of an ocean basin or how it became integrate into Anjouan .
