Harmotome


Harmotome		\|(Ba_0.5,Ca_0.5,K,Na)₅(H₂O)₁₂\| [Al₅Si₁₁O₃₂]

Morphology:
	Commonly as interpenetrating twins in groups or radiating aggregates. Twins repeated on {001}, {021}, {110}, may simulate a pseudotetragonal prism or a dodecahedron.

Physical properties:
	Cleavage: {010} distinct, {001} poor. Fracture: uneven to subconchoidal. Hardness: 4.5. D = 2.41 to 2.47 gm/cm³. Luster: vitreous. Streak: white.
			Twinned harmotome crystals Andreasberg, Harz, Germany. Width of image 15 mm. (© Volker Betz)
Optical properties:
	Color: colorless to gray, yellow, pink, brown; colorless in thin section. Biaxial (+). α = 1.503 - 1.508, β = 1.505 - 1.509, γ = 1.508 - 1.514, δ= 0.005 - 0.006, 2Vz = 80°. X˄a = 63°-67°, Z = b, O.A.P. \|\| (010). Dispersion: weak, crossed.

Crystallography:
	Unit cell data: a 9.869, b 14.139, c 8.693 Å, β 124.81°. Z = 1, Space group P2₁/m. (Rinaldi et al. 1974).



Name:
	Harmotome was named by Haüy (1801), renaming andreasbergolite (also known as andéolite) of Delamétherie (1795). The type locality is Andreasberg, Harz, Germany. The name comes from the Greek armos, a joint, and tome, to cut, referring to the morphology of twinned crystals. The name was retained by the Zeolite Subcommittee, because of historical precedence and usage. Wellsite has been used for compositions intermediate between phillipsite and harmotome. The name was discredited by Coombs et al. (1997) and should no longer be used.

Crystal structure:
	The basic building unit of the harmotome framework is a chain of doubly connected 4-rings, linking in the UUDD arrangement, generally known as double crankshaft (dcc in PHI). The true space group of harmotome (and the phillipsite series minerals) is still a subject of debate. Recent X-ray and neutron single-crystal structure refinements between 15 and 293 K confirm the centric space group P2₁/m for harmotome (Stuckenschmidt et al. 1990) as proposed by Rinaldi et al. (1974). There are, however, hints of acentricity (space group P21 or even P1), indicated by piezoelectricity (Sadanga et al. 1961) and optical domains (Akizuki 1985). There are three types of channels confined by eight-membered rings of tetrahedra, one parallel to the a-axis (aperture 3.6 Å), shown in the accompanying figure, one parallel to the b-axis (aperture 4.3 x 3.0 Å), and another parallel to the c-axis (aperture 3.3 x 3.2 Å). The double crankshaft chains run parallel to the a-axis (see PHI). Site C1 (red) occupied by Ba is located on the mirror plane and is coordinated on each side with two framework oxygen anions. The other cation site, C2, is coordinated with one framework oxygen and several water molecules, and is partially filled with minor Ca and Na.


Chemical composition:

Harmotome samples from epithermal veins show minor variation in Si and Ba contents. TSi averages close to 0.710, and the Ba content approaches two cations per unit cell, almost filling the K-Ba site (C1). Other non-framework cations are Ca, Na, or K; there appears to be no crystal chemical preference.


Occurrences:
	Harmotome is much less common than any of the phillipsite species for the obvious reason that the essential barium is less abundant in near surface waters. Although there are rare occurrences in sediment and basalt cavities, harmotome is best developed in epithermal veins. Harmotome in sedimentary rocks. Harmotome is a rare constituent of sediment and sedimentary rocks. Some of the early reported occurrences involve a mineral that under new definitions does not have sufficient barium. For example, the harmotome reported in the Big Sandy Formation of Arizona (Sheppard and Gude 1973) is now considered barian phillipsite-Na. Deep Sea Sediment. Harmotome has been reported from many localities in the Pacific basin, in some cases associated with phillipsite in pelagic clays (Goldberg and Arrhenius 1958 and Arrhenius 1963). It is uncertain how much harmotome actually exists in these sediments because determinations were made with X-ray powder diffraction methods, and few crystals were chemically analyzed. Goldberg and Arrhenius (1958) reported BaO contents between 3 and 15%, indicating that at least some harmotome is indeed present. Cavities of basaltic rocks. Because of its composition, harmotome rarely occurs in basalt cavities, and analyses of some reported harmotome in basalt, such as at the Giant’s Causeway, Northern Ireland, show that the mineral is actually a barian phillipsite. Some notable exceptions are the long known occurrences in the Idar-Oberstein area, Rhineland-Pfalz, where harmotome is associated with calcite in quartz-lined geodes in basalt (Leonhard 1812), such as those at Steinbruch Setz. Other basalt occurrences are the Zeilberg quarry near Maroldsweisach, Franconia, Bavaria; near Höwenegg , Hegau, Germany; and near Selva di Trissino, Vicenza, Italy (Passaglia and Bertoldi 1983). Deuteric or hydrothermal veins. Typical harmotome occurrences are in fissure veins of epithermal lead-zinc-silver ore deposits. At several mines at Andreasberg, Harz Mountains, Germany harmotome occurs on quartz, calcite, galena and other minerals (Hintze, 1897 and Tschernich, 1992). Exceptional crystals up to 2.5 cm across occur with apophyllite-(KF), calcite, and pyrite in the Korsnäs Lead Mine near Vassa, Finland (Sahama and Lehtinen 1967). In Scotland harmotome occurs in several mines at Strontian, where it is associated with strontianite and brewsterite in veins with calcite, barite, galena, and sphalerite (unpublished data of J. Landless and of B. Jackson, quoted in Tschnerich, 1992). Harmotome has been found in witherite veins in the old Pen-y-clun lead mine, Llanidos, Dyfed, central Wales (Morgan and Starkey 1991). In Norway large crystals of harmotome occur with calcite, pyrite, and native silver on gneiss at the Anne Sophie Mine, Kongsberg. In a similar setting harmotome and heulandite occur with native silver at Batopilas, Chihuahua, Mexico. Harmotome has also been reported from alteration zones associated with veins and dikes cutting serpentinite, such as Glen Riddle, Delaware County, Pennsylvannia (Meier, 1939) and at Hrubsice near Moravsky Krumlov, Western Moravia, Czech Republic (Černý and Povondra, 1965). Crystals of harmotome occur in thin fissures in altered dolerite at Odarslov, Skane, Sweden (Hansen 1990). It is in late stage phase in pegmatitic veins, breccia, and miarolitic cavities in nepheline syenite at Mont Saint-Hilaire, Québec. Harmotome occurs in carbonatite and hydrothermal veins in the Khibina massif, Kola Peninsula, Russia (Zaitzev et al. 1992). It was also found in a pegmatite of the Lovozero massif, where it occurs with stronianite, natrolite, and pyrite in the Catapleiitovoye pegmatite at Alluaiv Mountain (Pekov 2000). For further descriptions of occurrences of harmotome, see Tschernich (1992).

References:
	Akizuki, M. 1985. The origin of sector twinning in harmotome. Am. Miner. 70, 822-828. Arrhenius, G. 1963. Pelagic sediments. In Hill, M.N., ed., The Sea, 3, Wiley Interscience, New York, 655-727. Černý, P. and Povondra, P. 1965. Harmotome from desilicated pegmatites at Hrubsice, western Moravia. Acta Univer. Carolinae Geol. 1, 31-43. Coombs, D.S., Alberti, A., Armbruster, T., Artioli, G., Colella, C., Galli, E., Grice, J.D., Liebau, F., Mandarino, J.A., Minato, H., Nickel, E.H., Passaglia, E., Peacor, D.R., Quartieri, S., Rinaldi, R., Ross, M., Sheppard, R.A., Tillmanns, E., and Vezzalini, G. 1997. Recommended nomenclature for zeolite minerals: Report of the Subcommittee on Zeolites of the International Mineralogical Association, Commission on New Minerals and Mineral Names. Can. Min., 35, 1571-1606. Delamétherie, J.-C. 1795. Théorie de la Terre 1. Chez Maradan, Paris France. Goldberg, E.D. and Arrhenius, G. 1958 Chemistry of Pacific pelagic sediments. Geochim, Cosmochim. Acta, 13, 153-212. Hansen, S. 1990. Harmotome from Odarslov, Skane, Sweden. Geol. Feren. Stockholm Forh. 112, 140. Haüy, R.-J. 1801. Traité de minéralogie 3. Chez Louis, Paris, France. Hintze, C. 1897. Handbuch der Mineralogie 2. Verlag Von Veit & Comp., Leipzig. Leonhard, C.C. 1812. Reise nach Idar Oberstein durch das Thal der Nahein. Leonhard und Selb: Mineralogische Sudien, erster Theil, 145-188. Meier, A.E. 1939. Association of harmotome and barium feldspar at Glen Riddle, Pennsylvania. Am. Miner. 24, 540-564. Morgan, D. and Starkey, R. 1991. Harmotome from Pen-y-clun mine, Llanidos, Dyfed, Wales. UK Jour. Mines & Minerals, 10, 4-6. Passaglia, E. and Bertoldi, G. 1983. Harmotome from Selva di Trissino (Vicenza, Italy). Perid. Mineral. 52, 73-82. Pekov, I.V. 2000. Lovozero Massif: History, Pegmatites, Minerals. Ocean Pictures Ltd., Moscow, Russia. 484 pp. Rinaldi, R., Pluth, J.J., and Smith, J.V. 1974. Zeolites of the phillipsite family. Refinement of the crystal structure of philliposite and hamotome. Acta Cryst., B30, 2426-2433. Sadanga, R., Marumo, F., Takéuchi, Y. 1961. The crystal structure of harmotome. Acta Crystallogr. 14, 1153-1163. Sahama, Th.G. and Lehtinen, M. 1967. Harmotome from Korsnäs, Finland. Mineralogical Magazine 36, 444-448. Sheppard, R.A. and Gude, A.J. 3rd. 1973. Zeolites and associated authigenic silicate minerals in tuffaceous rocks of the Big Sandy Formation, Mohave County, Arizona. U.S. Geol. Surv., Prof. Paper 830, 36 pp. Stuckenschmidt, E., Fuess, H. and Kvick, Å. 1990. Investigation of the structure of harmotome by X-ray (293 K, 100K) and netron diffraction (15 K). Eur. Jour. Mineral., 2, 861-874. Tschernich, R.W. 1992. Zeolites of the World. Geoscience Press, Phoenix, Arizona. 563 pp. Zaitzev, A.N., Menshikov, Yu.P., & Yakoventchuk, V.N. 1992. Barium zeolites from Khibiny alkaline massif. Zap. Vses. Miner. Ob. 121, 54-61.