Natural "white" hydrogen (H2). There's virtually no pure H2 on Earth because it's so reactive. According to the US Department of Energy "although abundant on earth as an element, hydrogen is almost always found as part of another compound, such as water (H2O) or methane (CH4)".
But there are curiosities about natural H2, also known as native H2 being generated by geological processes. Emanations of H2 have been observed in many places and subsurface accumulations drilled “by chance”.
According to an article at Science Business "one such pool was found in Mali in the 1980s ... Today, the well gives out 98% pure hydrogen and has not recorded any decrease in production since extraction started in 2012."
There might be enough natural H2 to meet burgeoning global demand, according to a U.S. Geological Survey (USGS) model presented in October 2022 at a meeting of the Geological Society of America .
Click at the image below ("fairy circles" in Brazil) for an article by Materia Rinnovabile, explaining about natural H2. Basically the main engine of natural H2 production is thought to be a set of high-temperature reactions between water and iron-rich minerals such as olivine, which dominate Earth’s mantle. One common reaction is the convertion of olivine into another mineral called serpentinite. In the process, the iron oxidizes, grabbing oxygen atoms from water molecules and releasing H2. Often this H2 reacts immediately with the CO2 in the atmosphere and precipitates as carbonate, which effectively makes the process a natural and spectacular carbon capture process.
Besides the Mali case mentioned above, now owned by the Canadian company Hydroma currently known locations of native H2 are Oman, Philippines, New Caledonia, the Pyrenees, hundreds of (precambrian) cratons in Russia and USA, and the "fairy circles" in Brazil, Canada, Australia and Namibia
By the way, the French energy company Engie has been exploring the potential of natural H2 since 2016. It started off with projects in Brazil where hundreds of sensors to monitor the flux of H2 were developed and installed in the São Francisco Basin, where significant percentages of H2 in the subsurface had already been found and where "fairy circles" are visible .
Emanations measured in Russia, USA and Brazil range 50 - 1900 kg/km2/day. To give perspective, the reservoir of a fuel cell vehicle such as a Toyota Mirai is filled with 5 kg.
