Class : Silicates
    Subclass : Tectosilicates
    Crystal system : Monoclinic
    Chemistry : BaAl₂Si₆O₁₆ 6H₂O
    Rarity : Quite common

The harmotome belongs to the group of zeolites. It is a barium zeolite especially present in hydrothermal barite veins, often with brewsterite, more rarely in geodes of volcanic rocks (basalts, phonolites and trachytes). Its name comes from the Greek harmos (assembly) and temnein (to cut) to emphasize the fact that its crystals are often twinned, separated by grooves and can separate easily. Its morphology is close to that of phillipsite, forming constantly twinned prismatic crystals, assembled into complex buildings with an orthorhombic or tetragonal appearance. Sometimes the crystals are grouped in clumps or radiated spherolites. The harmotome is colorless or white, sometimes tinged with reddish or brownish.

Main photo : Harmotome from Thomaston, Connecticut, USA © Harold Moritz

Twins are common and repeated on {001}, {021} and {110}, which can form crosses and grooved crystals.

No fakes recorded for this mineral species.