On a windswept lava field in southwestern Iceland, 72 steel-clad collector units now hum around the clock, drawing carbon dioxide out of the open air. The facility is called Mammoth, and when Swiss company Climeworks began its phased startup in May 2024, it became the largest direct-air-capture (DAC) plant on Earth. By June 2026, all collector modules are operational, and the system is designed to remove up to 36,000 metric tons of CO2 per year. That gas does not get pumped into a cavern or sold to a bottling company. It gets turned into rock.
How atmospheric CO2 becomes stone
The mineralization process at Mammoth’s core was developed by the CarbFix project, a research effort born at the University of Iceland. The concept is deceptively simple: dissolve captured CO2 in water, then inject the carbonated solution deep into basalt bedrock. Underground, the dissolved carbon reacts with calcium, magnesium, and iron in the basalt to form solid carbonate minerals.
A landmark 2016 study published in Science, led by geochemist Juerg Matter and indexed by the U.S. Department of Energy, demonstrated that more than 95 percent of injected CO2 mineralized in under two years at the CarbFix pilot site. That finding upended a longstanding assumption in geology: that trapping carbon in rock required centuries or millennia. The reaction, it turned out, could happen on an industrial timeline.
CarbFix2, an EU-funded scale-up project operating under Grant Agreement 764760, then connected Climeworks’ air-capture hardware directly to the mineralization chain at the Hellisheidi geothermal site. The European Climate, Infrastructure and Environment Executive Agency confirmed the pairing in its official project description, noting that the demonstration integrates novel air-capture technology with subsurface mineralization to create an end-to-end carbon removal system. Geothermal energy from the site powers the collectors, and the surrounding basalt provides the injection target. Mammoth is the largest version of that integrated system built to date.
Putting the numbers in perspective
Mammoth’s predecessor, a smaller plant called Orca, launched at the same Icelandic site in 2021 with a design capacity of roughly 4,000 tons of CO2 per year. The jump to 36,000 tons represents a ninefold increase in throughput, a meaningful engineering milestone. But global CO2 emissions run to approximately 37 billion metric tons annually, according to the International Energy Agency. Mammoth’s full annual output, if verified, would offset roughly one millionth of that total.
Cost is the other sobering figure. Independent estimates for current DAC technology range from roughly $600 to over $1,000 per ton of CO2 removed, depending on energy source and plant design. The U.S. Department of Energy’s Carbon Negative Shot initiative has set a target of $100 per ton, but no operating facility has publicly demonstrated costs near that level. Climeworks has not released audited per-ton figures for the full capture-to-mineralization chain at Mammoth, and the EU grant documentation for CarbFix2 describes technical objectives without publishing independently verified cost data.
Those economics matter because DAC is not the only carbon removal option on the table. Reforestation, enhanced rock weathering, biochar, and ocean-based alkalinity enhancement all compete for funding and policy support. Each has trade-offs in permanence, scalability, and land use. What sets basalt mineralization apart is durability: carbonate rock is stable on geological timescales, meaning the stored carbon will not leak back into the atmosphere through a wildfire, a drought, or a change in land management.
What remains unproven
Several important gaps persist in the public record. No independently audited dataset of injection volumes or verified mineralization totals from Mammoth has been published as of mid-2026. The roughly two-year mineralization timeline established in the 2016 Science paper came from smaller-scale field trials. Whether that rate holds when injection volumes increase by an order of magnitude is an open question that only operational data from Mammoth and future plants can answer.
Verification protocols also need scrutiny. Multiple companies, including Microsoft and Shopify, have purchased carbon removal credits from Climeworks. But the specific methods used to confirm that a given ton of CO2 has actually mineralized underground, rather than simply been injected, are not detailed in publicly available institutional summaries. For corporate buyers staking net-zero pledges on these credits, transparent third-party verification is essential. A credit is only as good as the proof behind it.
Meanwhile, competition is intensifying. In West Texas, a joint venture between Occidental Petroleum’s 1PointFive subsidiary and Carbon Engineering broke ground on Stratos, a DAC facility designed to capture up to 500,000 tons of CO2 per year. Backed by the U.S. DOE’s Regional Direct Air Capture Hubs program and bolstered by the 45Q federal tax credit, Stratos and similar American projects could dwarf Mammoth’s output if they reach full operation. The Icelandic approach stores carbon in basalt; the Texas model plans to inject CO2 into deep saline formations, a different geological strategy with its own verification challenges.
Where the science is strong and where it is not
The peer-reviewed foundation beneath Mammoth is unusually solid for a climate technology at this stage. The 2016 Matter et al. paper (DOI: 10.1126/science.aad8132) provided field measurements showing rapid basalt mineralization. The CarbFix2 project added institutional documentation of the engineering chain from air capture to mineral storage. These are primary scientific and governmental records, not promotional materials.
News coverage of Mammoth, including a widely cited Washington Post report from its May 2024 opening, adds useful context about the facility’s relative size and market position. But readers should note that annual capacity figures and cost projections in media reports often trace back to company statements rather than independently audited data. The gap between what a plant is designed to capture and what it verifiably mineralizes in practice is the difference between an engineering target and a proven industrial process.
What happens next will define the technology
The science behind Mammoth works. Basalt mineralization converts atmospheric CO2 into stable rock on a timeline measured in months, not millennia. The engineering works too: Climeworks has built, shipped, and assembled modular collector units at increasing scale across two generations of plants. What has not yet been demonstrated is whether the economics can close the gap between a $600-plus cost per ton and a price point that governments and corporations will pay at the volumes the climate crisis demands.
The next few years of operational data from Mammoth, and from competitors like Stratos, will determine whether direct air capture becomes a serious tool in the carbon removal portfolio or remains a technically impressive but financially constrained niche. Independent audits of mineralization rates, transparent cost reporting, and rigorous credit verification will separate the proven from the promised. The rock does not lie. The question is whether the ledger will match.
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*This article was researched with the help of AI, with human editors creating the final content.
