Mafix raises $5.4m to speed up enhanced rock weathering on farmland
Stanford spinout Mafix raised $5.4m on 20 August 2026 to scale enhanced rock weathering, a silicate fertiliser that removes CO2 and feeds crops.
Photo by dayong tien on Pexels
Mafix, a startup built on chemistry developed at Stanford University, announced on 20 August 2026 that it had raised $5.4 million in pre-seed funding to commercialise a silicate mineral product designed to remove carbon dioxide and act as a crop fertiliser at the same time. The approach is a variant of enhanced rock weathering, and the company’s pitch is speed: it heats silicate minerals with limestone in cement kilns to make a material that dissolves in soil within a single growing season rather than over years.
The round was led by Azolla Ventures, with Counteract VC, the Astera Institute, Plug and Play Ventures, Impact Science Ventures and a Dutch family office. The company’s announcement carries a Seattle dateline. Mafix was co-founded by Jade Marcus, chief executive and a chemical engineering PhD student at Stanford, and Matthew W. Kanan, a professor of chemistry at Stanford and director of the university’s TomKat Center for Sustainable Energy. Marcus holds a chemical and biomolecular engineering degree from Georgia Tech and worked as an engagement manager at McKinsey before joining Kanan’s lab in 2023.
How enhanced rock weathering works, and what Mafix changes
Enhanced rock weathering speeds up a reaction that happens naturally over geological time. Crushed silicate rocks such as basalt or olivine are spread on farmland; rainwater and dissolved CO2 attack the minerals, and the carbon ends up locked in stable bicarbonates that wash to the ocean or stay in soil. The MIT Climate Portal explainer on the method notes that natural rock weathering “takes place over many millions of years”, which is why the field is built around ways to accelerate it.
The measurement problem follows directly from that slowness. When minerals dissolve gradually, the carbon-removal signal is hard to separate from ordinary variation in soil and water chemistry, so verification runs for years and costs money every year. Marcus put the point to AgFunderNews this way: “What you hear a lot about in the ERW space is that there’s not enough signal to noise.”
Mafix’s process heats a mix of silicate minerals and limestone in a cement kiln, triggering a solid-state ion exchange that produces more reactive calcium-magnesium silicates. The underlying chemistry was published by Yuxuan Chen and Matthew W. Kanan in the paper “Thermal Ca2+/Mg2+ exchange reactions to synthesize CO2 removal materials”, which appeared in Nature on 19 February 2025 (volume 638, pages 972 to 979). The abstract reports that calcium carbonate and calcium sulfate react quantitatively with magnesium-rich silicates including olivine, serpentine and augite to form Ca2SiO4 and MgO, and that on exposure to wet ambient air the magnesium oxide is “partially converted into a Mg carbonate within weeks, whereas the input Mg silicate shows no reactivity over 6 months”. The paper also estimates the process could require less than 1 MWh per tonne of CO2 removed, roughly half the energy of leading direct air capture.
What the field data shows
Stanford’s own account of the spinout, published in May 2026, cites an independent study finding the Mafix material captured an average of 2.7 tonnes of CO2 per hectare in six months, against 0.03 tonnes per hectare for crushed basalt over the same period. The same article reports that greenhouse trials of rice at Louisiana State University showed a 50 per cent increase in grain yields using Monti, the company’s product name.
Marcus separately told AgFunderNews that mesocosm experiments, run in enclosed systems that let researchers track inputs and outputs precisely, “removed over 4.7 tons of CO2 in 10 weeks, whereas basalt and olivine had close to zero negligible removal”. That figure and the company’s claim of a 126 per cent calcium carbonate equivalent, which would make the material a stronger acid neutraliser than agricultural lime by weight, come from the company and have not been independently published.
The agronomic case rests on silicon. Most silicon in soil is not in a form plants can take up, and Mafix says its material supplies plant-available silicon, which can stiffen plant tissue and help release phosphorus otherwise bound in soil. Marcus stressed that more field data is needed before the company makes agronomic claims.
Where the money goes and what carbon credits pay
The $5.4 million covers production of about 1,000 tonnes of material next year, enough for roughly 1,000 to 2,000 acres depending on application rate, and gives the company runway for at least two growing seasons of trials. Marcus had previously secured non-dilutive research funding at Stanford through the TomKat Center and the Stanford Sustainability Accelerator; she put the figure at about $1.5 million in the AgFunderNews interview, while her Forbes 30 Under 30 profile records about $1.4 million.
| Round detail | Figure |
|---|---|
| Amount raised | $5.4 million pre-seed |
| Announced | 20 August 2026 |
| Lead investor | Azolla Ventures |
| Other investors | Counteract VC, Astera Institute, Plug and Play Ventures, Impact Science Ventures, a Dutch family office |
| Production target | About 1,000 tonnes next year |
| Area covered | Roughly 1,000 to 2,000 acres |
Source: Mafix announcement via GlobeNewswire, 20 August 2026; AgFunderNews, 20 August 2026.
The revenue model runs on carbon credits first. Mafix expects credit sales to fund the business initially so it can supply farmers with the product at no cost, then wants the agricultural product to pay for itself. That matters because credit prices are the binding constraint. Frontier Climate’s enhanced weathering pathway page records a current price range of $270 to $500 per tonne and an average offtake price of $362 per tonne. AgFunderNews cited a range of $200 to $500 per tonne for the same source; Frontier’s own published floor is $70 higher. Frontier also puts the potential of surficial mineralisation at more than 10 gigatonnes a year at $80 to $120 per tonne, the band Mafix says it is aiming for.
| Frontier Climate enhanced weathering portfolio | Figure |
|---|---|
| Tonnes contracted | 333,000 |
| Dollars contracted | $121.0 million |
| Companies contracted | 8 |
| Average offtake price | $362 per tonne |
| Current price range | $270 to $500 per tonne |
Source: Frontier Climate, enhanced weathering pathway page, retrieved 24 August 2026.
Background
Enhanced rock weathering has consolidated over the past two years. Terradot launched in December 2024 with $58.2 million and agreements covering close to 300,000 tonnes, then agreed to acquire the assets of Eion on 6 February 2026, folding in Eion’s contracts for more than 100,000 carbon removal credits. Financial terms were not disclosed. In June 2026, Alt Carbon signed a three-year offtake with Microsoft for 36,920 tonnes from its Darjeeling Revival Project in eastern India, according to CDR.fyi’s monthly recap.
The measured evidence base is also growing outside the commercial sector. Winss Solutions has reported on a study in which rock dust and soil microbes boosted carbon in a new UK forest, and on the wider market for land-based removal, including Mombak’s delivery of Amazon carbon credits two years early and nature-based removal deals signed by Google and Tencent. Measurement remains the shared bottleneck across all of these routes, which is the gap the EarthOptics and Cquester soil carbon partnership is also aimed at.
Against that backdrop, durable carbon removal as a whole still sits at about 0.002 gigatonnes of CO2 a year, per the third edition of the State of Carbon Dioxide Removal report cited by CDR.fyi in July 2026. Mafix’s 1,000-tonne production run is a trial batch measured against that total, and the company has said it needs larger field trials before it makes claims about yields.
Sources: Mafix via GlobeNewswire; AgFunderNews; Nature; Stanford University; Stanford Department of Chemistry; Frontier Climate; MIT Climate Portal; Azolla Ventures; Terradot via Business Wire; CDR.fyi; Forbes
Featured image: photo by dayong tien on Pexels (free Pexels license).
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I specialize in sustainability education, curriculum co-creation, and early-stage project strategy. At WINSS, I craft articles on sustainability, transformative AI, and related topics. When I’m not writing, you’ll find me chasing the perfect sushi roll, exploring cities around the globe, or unwinding with my dog Puffy — the world’s most loyal sidekick.
