MgO-based cements offer a low-carbon alternative to traditional Portland cement as they can be produced from Mg-silicate minerals with renewable energy. As interest in these alternative binders develops, understanding of their composition and mechanical properties becomes crucial. During hydration, magnesium silicate hydrates (M-S-H) form. While the thermodynamic properties and hydration mechanisms of these phases have been studied, research on their mechanical behavior remains limited. This study investigates the microstructural and elastic properties of M-S-H pastes at the micrometer-scale after undergoing various production protocols. The impact of using carbonates as accelerators on mechanical properties was studied. Detailed chemical (XRD, TGA, SEM/EDS), microstructural (water saturation), and mechanical (indentation) analyses were conducted. When carbonates are used in the curing water, brucite is eventually consumed, but porosity increases. Overall, the plain strain indentation modulus of the M-S-H pastes is highly dependent from the porosity and the curing with carbonates doesn’t change the elastic properties.