Mafix raises $5.4M pre-seed for rock-based carbon-removing fertilizer

Mafix, the latest spinout from a Stanford chemistry lab, is making rocks weather on purpose. It was founded in 2026 by Jade Marcus and chemistry professor Matthew Kanan. The company has raised $5.4 million in a pre-seed round led by Azolla Ventures, with Counter participating, according to ESG Today.

Mafix converts inert silicate rocks into fast-weathering minerals. Applied as fertilizer, those minerals release nutrients for crops while pulling carbon dioxide out of the air as stable bicarbonate. The reaction, Mafix says, completes within a single growing season — an answer to the standard critique of enhanced rock weathering, which crushes basalt and waits on slow natural chemistry.

Mafix says its drop-in process can run in existing cement kilns, using spare capacity rather than requiring new plants. The economics of carbon removal hinge on cost, and a process that borrows idle industrial assets is more likely to fetch fertilizer prices than carbon-credit prices.

The new capital pays for a 1,000-ton commercial demonstration and for extending the conversion process to other feedstocks and markets beyond agriculture. Marcus calls the alkalinity trapped in silicate rocks "one of the largest untapped resources on the planet."

This pre-seed is a different scale from the 50,000-ton biomass removal offtake Senken signed this week. The bet is also different: build carbon-removal capacity inside a mature industry, then hope farmers buy the bundle.