Current carbon capture and utilization (CCU) technologies require high energy input and costly catalysts. Here, an effective pathway is offered that addresses climate action by atmospheric CO2 sequestration. Industrially relevant highly reactive alkali cellulose solutions are used as CO2 absorption media. The latter lead to mineralized cellulose materials (MCM) at a tailorable cellulose-to-mineral ratio, forming organic-inorganic viscous systems (viscosity from 102 to 107 mPa s and storage modulus from 10 to 105 Pa). CO2 absorption and conversion into calcium carbonate and associated minerals translate to maximum absorption of 6.5 gCO2 gcellulose−1, tracking inversely with cellulose loading. Cellulose lean gels are easily converted into dry powders, shown as a functional component of ceramic glazes and cementitious composites. Meanwhile, cellulose-rich gels are moldable and extrudable, yielding stone-like structures tested as artificial substrates for coral reef restoration. Life Cycle Assessment (LCA) suggests new CCU opportunities for building materials, as demonstrated in underwater deployment for coral reef ecosystem restoration.