Mafix, a California start-up built on chemistry from Stanford University, has raised $5.4 million in pre-seed funding to scale a new form of enhanced rock weathering that makes silicate minerals break down far faster on farmland. The company says the material removes carbon, simplifies the measurement and verification of that removal, can raise yields and may eventually cut fertiliser costs.

Azolla Ventures led the round, with Counteract VC, Astera Institute, Plug and Play Ventures, Impact Science Ventures and a Dutch family office taking part. Cofounder Jade Marcus said the money will pay for 1,000 tonnes of product for trials across the United States next year, enough for roughly 1,000 to 2,000 acres depending on the rate, and gives the company runway for at least two growing seasons. Marcus had earlier secured $1.5 million in non-dilutive funding to develop the technology at Stanford.

Enhanced rock weathering spreads crushed silicate rock such as basalt or olivine on fields, where it reacts with rainwater to bind atmospheric carbon dioxide into stable bicarbonates while improving the soil, much as agricultural lime does. Mafix, based on work by Matt Kanan, PhD, and PhD candidate Marcus, goes a step further: it heats silicate minerals with limestone in cement kilns, triggering a solid-state ion exchange that yields calcium-magnesium silicates that dissolve rapidly once spread.

That speed matters for the carbon business. Slow weathering produces a removal signal hard to tell from natural variation in soil and water chemistry, so verification is expensive and repeated year after year. “By having something that can weather quickly, you’re able to get over that signal to noise barrier,” Marcus told AgFunderNews. A 2025 Nature paper from Kanan’s lab showed one silicate rock fully carbonated in seven weeks, and mesocosm trials removed more than 4.7 tonnes of CO2 in ten weeks while basalt and olivine removed close to none over the same period.

The agronomic case rests on silicon and alkalinity. Most silicon in soil is not available to plants; Mafix says its material supplies it in usable forms that strengthen tissue and improve resilience to drought, pests, fungal disease and lodging, and can free phosphorus bound in the soil while helping plants use nitrogen more efficiently. The product has a calcium carbonate equivalent of 126 per cent, more acid-neutralising capacity than ag lime by weight. Marcus stressed that larger field trials are needed before agronomic claims are made.

Mafix plans to use spare capacity at cement plants, which already hold limestone, processing silicate rock sourced within 20 to 60 miles. The kiln step adds cost and emissions, but Marcus said the net effect is to triple the alkalinity available for carbon removal. Carbon credits, which currently fetch $200 to $500 a tonne for enhanced rock weathering, will fund the business at first so farmers receive the product free; longer term the company wants the agricultural product to pay its own way, for instance by replacing the inert filler in NPK blends. It believes it can eventually deliver removal for under $100 a tonne.

“Weathering rocks on land is one of the simplest ways to remove carbon from the atmosphere, but in our experience the payoff for landowners has often not been good enough,” said Counteract VC partner Andrew Shebbeare, noting that Mafix minerals weather in a single season. Marcus, a Georgia Tech chemical engineer who worked in McKinsey’s sustainability practice before Stanford, put it plainly: “You can’t have a product that solely relies on the carbon market.”

Source: AgFunderNews