DescriptionBrimstone is a US startup that has developed a process to manufacture Portland cement with a negative carbon footprint. Instead of limestone, it uses abundant, carbon-free calcium silicate rocks, thereby eliminating the emissions associated with limestone decomposition. Its technology produces clinker and supplementary cementitious materials (SCMs) from a single raw material and, during calcination, forms magnesium compounds that capture carbon dioxide, meaning the cement can potentially be carbon-negative. The resulting product meets the ASTM C150 standard for Portland cement and integrates into the existing supply chain without altering concrete performance. Brimstone aims to scale this method to decarbonise the cement industry and, additionally, produce metallurgical-grade alumina.