Formula: Ba2(Si12Al4)O32.12H2O
Tectosilicate (framework silicate), phillipsite subgroup, zeolite group, forms a series with phillipsite-Ca
Crystal System: Monoclinic
Specific gravity: 2.41 to 2.47 measured, 2.448 calculated
Hardness: 4 to 5
Streak: White
Colour: Colourless, white, grey, pink, yellow, brown
Common impurities: Na,Ca

Sedimentary environments (rarely)
Metamorphic environments
Basaltic cavities

Harmotome occurs in basaltic cavities associated with calcite and rarely natrolite. It has also been reported in tuff associated with calcite, laumontite and pyrite (DHZ 4 p398).

At Nisikkatch lake, Saskatchewan, Canada, harmotome occurs in veins in gneiss associated with microcline variety hyalophane and albite (DHZ 4 p398).

In northern Italy harmotome occurs in graphite lenses in gneiss with quartz, sphalerite and galena (DHZ 4 p398).

In the Ural mountains, Russia, harmotome occurs in bauxite with kaolinite and halloysite (DHZ 4 p398).

At Snailbeach mine, near Minsterley, Shropshire, England, UK, harmotome occurs with calcite (RES p273).

At the Struy lead mines, Inverness, Scotland, UK, harmotome occurs in hydrothermal veins with sphalerite, baryte and calcite (DHZ 4 p398).

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