Magnesium carbonate is sparingly soluble in water; its solubility is extremely low, so it is often described in general terms as "insoluble" or "hardly soluble."
Very low solubility: The solubility in water is only 0.02 g/100 g at 15°C and approximately 0.025 g/100 g at 25°C.
Varied descriptions: Some sources state it is "insoluble in water," while others describe it as "slightly soluble"; in reality, the solubility is so low that no obvious dissolution is observed.
Readily soluble in acids: Although poorly soluble in water, it dissolves in dilute acids, decomposing to release carbon dioxide gas upon contact.
Aqueous solution is weakly alkaline: The small amount of dissolved magnesium carbonate imparts a weakly alkaline reaction to the water.