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In order to build the relationship between inherent crystallographic characteristics and crystal morphology of hydromagnesite, the energies, structures, and growth properties of hydromagnesite surfaces were theoretically investigated by density functional theory calculations and molecular dynamic simulations. Scanning electron microscopy results show that the flower-like hydromagnesite crystal is formed by the self-assembly of sheet-like crystallites. Surface energy calculations confirm that the most stable (100) surface corresponds to the plane of the sheet-like crystallite and the (011) surface and other surfaces refer to the edges of the crystallite. During surface relaxation, electrons transfer from Mg atoms to O atoms, leading to the decrease of the Mg−O bond length, which contributes to the formation of a more stable surface structure. The growth unit (GU) is characterized by one OH group, one HCO 3 group, and three coordinated H 2 O molecules. In all single-point adsorption modes, the GU loses one H 2 O molecule, making the structure of the adsorbed GU closer to the bulk crystal structure with fewer water molecules. For the (100) surface, the nearly same possibility of all adsorption modes is conducive to the growth of the (100) surface into the plane of the sheet-like crystallite, and it is still the most stable surface after adsorptions. This work can provide new insights and methods for studying the growth mechanism and morphology control of the hydromagnesite crystal.

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