He says that he and his group have ruled out other possible explanations for the skewed ratio of carbon isotopes, such as decomposition of the mineral siderite.

The Xinjiang meteorite weighs 17.8 tons and is made of siderite, or iron carbonate, according to a report in the Chinese news media that cited an official research center.

They found that silicate minerals, such as olivine and feldspar, had interacted with CO2-rich liquid water to form siderite crystals.

There it forms a large deposit, in a granitic vein running through gneiss, and is accompanied by quartz, siderite, galena, blende, chalcopyrite, &c.

The entrance is flanked by large chunks of ironstone, or siderite, and features crushed brick paving, a reference to the brickyard that operated there for much of the 20th century.