Like direct air capture with pore space storage (DACPS), direct air capture with carbon mineralization storage (DACCM, pronounced dăk-c-m) involves capturing CO₂ gas from the atmosphere, compressing the CO₂ gas to a semi-liquid state, and then injecting it underground for long-term storage.
 DACCM differs from DACPS in that the injection target is basalt or similar igneous rock, in contrast to sedimentary rock such as sandstone, a common injection target in DACPS.

 In DACCM, carbon and oxygen in the injected CO₂ chemically react with calcium in the basalt to form calcium carbonate (CaCO3), limestone. So, in DACCM, the CO₂ is converted to solid rock for long-term storage, in contrast to DACPS which stores CO₂ as a semi-liquid fluid physically trapped in the pore spaces of rock.

 DACCM is restricted to geographic areas where basalt lava flows or similar igneous rocks have been deposited. In contrast, DACPS is restricted to areas underlain by sedimentary rocks (sandstone or limestone, which commonly are oil and gas producing areas).

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DACCM has six basic steps (note that steps 1 through 4 are the same as for DACPS):

1. Extract CO₂ gas from the atmosphere in a plant where fans blow air through an air contactor and CO₂ molecules attach to either a liquid solvent or a solid sorbent (the two main types of DAC plants).
2. Release the CO₂ from the solvent or sorbent using heat and/or water. The solvent/sorbent is reused.
3. Liquify extracted CO₂ by compressing.
4. Transport the liquified CO₂ via pipeline to underground injection wells.
5. Inject the CO₂ deep (>800 meters) into the ground into a basalt layer or similar igneous rock. Basalt is dense and it must have enough fractures or joints in it to allow the the invasion of the injected CO₂. Also, the injection layer must be overlain by relatively impermeable rock for preventing upward flow of the buoyant CO₂ toward the land surface.
6. Following the path of least resistance underneath the less permeable layer, the injected CO₂ flows laterally, outward from the injection well, fingering through fractures and joints in the basalt, reacting with the basalt along the flowpath to form limestone.

 DACCS (direct air capture with carbon sequestration) is the traditional, widely used expression for both carbon mineralization storage and pore space storage.
 Distinguishing between DACPS and DACCM — rather than lumping them together as DACCS — helps in understanding the geographic distribution of DACPS and DACCM projects, evaluating their CO₂ leakage potential and storage durability, and understanding the commercial development DACCS and DACCM as CDR methods.

 DACCM, as one of the two types of DACCS, is viewed by many as a tool that is necessary for the world to reach net zero during the transition from fossil fuels to energy sources that have low or zero greenhouse gas emissions.
 DACCM may serve as an alternative to DACPS in geographic areas where sedimentary rocks are lacking, but basalt or similar rocks are present.
 DACCS (which includes both DACCM and DACPS) is widely criticized for the potential to prolong the use of fossil fuels and the potential for hindering the scale-up of low emissions energy sources such as solar.
 A general criticism of many carbon dioxide removal projects is that in society's pursuit of net zero emissons, it would be more energy- and cost-efficient to replace fossil fuels very soon with renewable energy sources such as solar and wind, than to continue burning fossil fuels and developing complex systems such as DACCS for capturing and storing the resulting CO₂ emissions.

 The only large-scale DAC plant that stores CO₂ underground relying on carbon mineralization (DACCM) is Climeworks' Mammoth Project in Iceland. Mammoth began operation in May 2024, with annual capture capacity of 36,000-tons of CO₂. As of early 2025, Mammoth is the largest DACCS plant in the world.
 Climeworks has also been operating a 4,000-ton per year demonstration-scale commercial DACCM project in Iceland since 2021, called the Orca Project.
 The only test of DACCM before Orca was a pilot project . . performed in 2009 by the U.S. Department of Energy, the Wallula Project, located in the western U.S. state of Washington where about 1,000 tons of purchased CO₂ were injected into basalt.
 In addition to the Mammoth DACCM plant, four other large-scale DACCM projects worldwide are in the planning stage (view table). Also, some of the DAC projects listed in the CDR.fyi database could possibly use carbon mineralization for storage (see CDR.fyi, search on DACCS). These projects have pre-sold carbon credits for future delivery to buyers who are trying to meet their companies' net zero goals by the year 2050 — a deadline consistent with many national net-zero goals. Investors and government incentives in the form of grants or tax credits help drive many of projects.

 Injecting CO₂ underground can cause earthquakes if injected with a high enough pressure to fracture rock underground. Semi-liquid CO₂ stored underground can leak to the land surface through an injection well or an old oil or gas well in the storage area if CO₂ degrades the steel well casing. CO₂ can also leak to the land surface if, prior to carbon mineralization, a flow pathway through a topseal layer of rock is dissolved by carbonic acid that is created when CO₂ dissolves in groundwater.
 CO₂ that has been converted to solid limestone underground has no risk of leakage from storage.

 DACCM has the same energy requirements as DACPS for capturing and compressing one ton of CO₂, an estimated 2.17 MWh/tCO₂, dropping to 1.44 MWh/tCO₂ by year 2050.
 For a 1-million-ton per year DACCM plant, the 1.44 MWh/tCO₂ equates to the annual energy use of 96,000 homes (assuming each home uses an average of 3.0MWh of energy annually).
 Energy would need to come from a low- or zero-carbon source for a DACCM project to be carbon negative (i.e., remove more carbon dioxide than the project produces). A cradle-to-grave life-cycle assessment of a project is necessary for verifying the project will be carbon negative.

 Like DACPS, DACCM costs include the costs of: CO₂ capture, compression, transport, underground storage, and monitoring. The total cost of removing and storing one ton of CO₂ using DACCS (either DACPS or DACCM) in 2020 was estimated to be between approximately €175 to €400 per ton of CO₂ removed ($204 - $467 USD). This cost has been projected to drop to roughly the €100 to €250 range ($117 - $292 USD) by the year 2050 due to gains from economy of scale and technology advances.

 The number of tons of CO₂ removed from the atmosphere and stored in a DACCM project can be measured using a flow meter at the injection wellhead.
 Monitoring is aimed at detecting leaks of CO₂ from the underground reservoir. Monitoring methods include monitoring wells, seismic mapping of the underground CO₂ plume, and CO₂ gas detectors installed in soil or on the land surface. Government regulations typically require an approved monitoring plan prior to approving a permit for a CO₂ injection well.
  Puro Earth, a Finland-based carbon credit registry company, has developed a protocol for verifying and certifying the amount of CO₂ removed in a carbon mineralization storage project. Puro Earth has certified carbon credits created by the Climeworks' Orca carbon mineralization project in Iceland.

 CO₂ stored in a geological formation (including a DACCM project) is considered to be virtually permanent (at least 10,000 years).

 DACCM, as well as the other geologic methods of CDR, are referred to as "novel" (new, unproven) methods of CDR — compared to conventional, proven CDR methods (e.g., biochar, bioenergy with carbon capture and storage, afforestation).
 A scenario has been described for the year 2050 in which the novel methods annually supply about 2 gtCO₂ of the total annual 10 gtCO₂ of CDR that will be needed then in order to limit global warming to 2^oC above pre-industrial levels (circa year 1850).
 Visualizing the potential scale of DACCM development in 2050: If DACCM supplies one-fourth (0.5 gtCO₂ per year) of the annual 2 gtCO₂, then 500 DACCM plants each with 1 million gtCO₂ annual removal capacity will be needed.