Chef and owner Johnny Hernandez addresses me through the steam rising from arrachera en salsa de tomatillo, a central Mexican speciality cooked and served in a molcajete - a mortar hewn from volcanic basalt whose design dates back to Mesoamerican times.

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The Giant's Causeway is made up of 40, 000 black basalt columns protruding from the sea.

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Japanese researchers say the basalt in NWA 011 suggests the body from which it did originate had a core of molten iron with an outer covering of silicon and aluminium that formed a basaltic crust.

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Marco notes that the nearest basalt outcrop was a few hundred meters from the site, and that the stones, which were three to six feet (one to two meters) in width, would have weighed over 200 pounds (90 kilograms) at times.

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