Harmotome Locality: St Andreasberg, St Andreasberg District, Harz Mts, Lower Saxony, Germany (Locality at mindat.org) Size: cabinet, 10.8 x 10.6 x 3.9 cm Harmot — Photo: Robert M. Lavinsky · CC BY-SA 3.0
Harmotome
A rare barium zeolite forming white, well-defined 'cross-twinned' monoclinic crystals among calcite and other zeolites.
Intro adapted from Wikipedia (CC BY-SA).
Harmotome is an IMA-recognized mineral species in the silicate class, with the chemical formula Ba₂(Si₁₂Al₄)O₃₂·12H₂O.
It crystallizes in the monoclinic crystal system (space group P2_1/m). It is a member of the Harmotome structural group.
Key properties: Mohs hardness 4.5; specific gravity 2.41–2.47; typically white or colorless or yellow or pink or brown; White streak; Vitreous luster; optically biaxial.
IMA symbol Hrm, IMA status: approved, named in 1801.
Of hydrothermal origin, in cavities in basalts, phonolites, trachytes; in gneisses, and in some ore veins.
It is found associated with Zeolites, calcite, leucite, hyalophane, strontianite, quartz, kaolinite, barite, pyrite, sphalerite, galena.
Its name comes from the Greek harmos, for a joint, and tome, for a cutting, as the twinned crystals may be divided.
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