Anjouan is a remote tropical island in the Indian Ocean that’s making headlines for being the location of one of the biggest geological mysteries of all time. The small island, which is located between Madagascar and the east coast of Africa, is 163 square miles, has lots of vegetation and has a population of approximately 277,000 people. Anjouan, which is one of the Comoro Islands, was created 4 million years ago from undersea volcanoes and has steep, mountainous terrain as well as beaches containing black sand.
Since the island was formed by volcanoes, it consists of a lava-derived rock called basalt, but that’s not all. There are sedimentary rocks which are lighter in color that are found all over the island and should not be there as they aren’t part of the volcanic rock that formed this island millions of years ago. The rocks are made from a type of sandstone called quartzite.
Cornelia Class, who is a geochemist at the Lamont-Doherty Earth Observatory at Columbia University, said, “It doesn’t look like anything that could have formed on an island like that,” adding, “There is nothing there that could form a quartzite.”
Class led an expedition to the island in order to further research the rocks and found that there was much more quartzite than expected as it made up nearly half of a mountain. The scientists searched around the town of Tsembehou and found large boulders of quartzite. Then they climbed up a ridge called Habakari N’gani and found that the top was made almost entirely of the substance. Some locals use the quartzite to sharpen knives, as pieces of it have made their way to the villages by travelling down rivers and stream beds.
Sometimes crust ends up in the ocean after breaking off of a continent, and since quartzite comes from continental crust, it somehow must have made its way into the ocean basin and was lifted up with the volcanic rock to form the island.
There is still much more research that needs to be done in order to explain how the quartzite ended up on a volcanically made island. First, the researchers need to find out how old the quartzite is and find out where exactly it originated from. While Class thinks that it originated from Madagascar or East Africa, the substance needs to be studied much more thoroughly to find out for sure. She also said that additional geochemical measurements of the volcanic rocks need to be conducted in hopes of figuring out the geological history of the island.
This is definitely an interesting and mysterious find, “This is what nature presents, sometimes,” Class stated, “It’s something we consider impossible, but then we find it, and once we find it, we have to explain it.”