43 Photos
Harmotome
Chemical Formula	(Ba0.5,Ca0.5,Na,K)5Al5,Si11O32·12(H2O)
Species	Silicates
Crystal System	Monoclinic
Mohs Scale	4-5
Specific Gravity	2.5
Color	Colorless, white, grey, pink, yellow, brown
Streak	White
Luster	Vitreous
Refractive Index	n = 1.503 - 1.508 n = 1.505 - 1.509 n = 1.508 - 1.514
Diaphaneity	Transparent, Translucent
Cleavage	Distinct/GoodDistinct on , poor on
Fracture	Irregular/Uneven, Sub-Conchoidal
Crystal Habit：Crystals elongate or tabular, frequently twinned.
Geological Setting：Cavities in basalts, phonolites, trachyites, gneisses and some hydrothermal veins.

Harmotome is a mineral, one of the rarer zeolites; a hydrated barium silicate with formula: (Ba_0.5,Ca_0.5,Na,K)₅Al₅,Si₁₁O₃₂·12(H₂O). It forms vitreous white well defined monoclinic crystals, often associated with calcite and other zeolites. It has a Mohs hardness of 4 to 5 and a specific gravity of 2.44 to 2.5.

Name and discovery

Named from the Greek words harmos (I combine) and temseis (I cut) 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.