Harmotome is a mineral, one of the rarer zeolites; a hydrated barium silicate with formula: (Ba0.5,Ca0.5,Na,K)5Al5,Si11O32·12(H2O).

It forms vitreous white well defined monoclinic crystals, often associated with calcite and other zeolites.

Named from the Greek words Ancient Greek: ἁρμός, romanized: harmos (a joint) and Ancient Greek: τέμνειν, romanized: témnein (to cut) by René Just Haüy in 1801[2] because the pyramid divides parallel to the plane that passes through the terminal edges.

It was first described in 1801 from an occurrence in the Harz Mountains, Lower Saxony, Germany.

Like other zeolites, harmotome occurs with calcite in the amygdaloidal cavities of volcanic rocks, for example, in the dolerites of Dumbartonshire, and as fine crystals in the agate-lined cavities in the melaphyre of Oberstein in Germany.