Abstract This life cycle assessment evaluates the environmental impacts of two emergent masonry blocks designed to serve as sustainable replacements for conventional masonry blocks. The emergent blocks offer the same strength, durability, and form as conventional structural concrete blocks, and include hollow cores to enable placement of reinforcement in accordance with standard construction practices. The first emergent block consists of stabilized engineered soil that is compacted to reduce the use of ordinary Portland cement and eliminate curing. The second block, which is also compacted, contains alkali activators that promote a geopolymerization reaction among naturally occurring aluminosilicate clays, eliminating the need for ordinary Portland cement. QuantisSuite 2.0 software is used to perform a cradle to gate life cycle assessment comparing the environmental impacts of the two blocks to conventional concrete blocks across a range of indicators. The compacted stabilized soil block offers 46% less embodied carbon than conventional concrete block, which it outperforms in all categories except water consumption. The compacted alkali-activated block reduces embodied carbon by 42% when compared to concrete block, but has a higher impact on ecosystem, water withdrawal and resources. In terms of ecosystem and health indicators, the compacted stabilized soil block is the preferred building block, while conventional concrete block architectural blocks are the most water efficient. As understanding of alkali activation improves and manufacturing of compacted block is optimized, further environmental benefits are possible in both stabilized soil block and the alkali-activated block.