What is "magnesium bicarbonate"

n. a bicarbonate that is a major cause of hard water

Magnesium bicarbonate or magnesium hydrogen carbonate, Mg( H CO), is the bicarbonate salt of magnesium. It can be formed through the reaction of dilute solutions of carbonic acid (such as seltzer water) and magnesium hydroxide (milk of magnesia).

Magnesium bicarbonate exists only in aqueous solution. To produce it, a suspension of magnesium hydroxide is treated with pressurized carbon dioxide, producing a solution of magnesium bicarbonate:

Mg(OH) + 2 CO → Mg(HCO)

Drying the resulting solution causes the magnesium bicarbonate to decompose, yielding magnesium carbonate, carbon dioxide, and water:

Mg + 2 HCO → MgCO + CO + HO