Harmotome
Harmotome is Ba2(Si12Al4)O32·12H2O, the barium member of the phillipsite series: twinned crystals to 4 cm, hardness 4.5, density 2.41–2.47, 18.97% barium.
Harmotome is Ba2(Si12Al4)O32·12H2O on the September 2026 IMA list: a monoclinic barium zeolite, the Ba-dominant member of the phillipsite series, commonly as interpenetrant twins to 4 cm, hardness 4.5, density 2.41–2.47. Worked, it is 18.97% barium, and on the sheet’s German and Scottish analyses barium is 70–75% of the extra-framework cations.
In short
- The species. The Handbook of Mineralogy sheet gives monoclinic crystals elongated ∥ [001] or tabular ∥ {010}, typically striated, commonly as interpenetrant twins to 4 cm, alone, in groups or radiating aggregates; {010} cleavage distinct; hardness 4.5; density 2.41–2.47; colourless, white, gray, yellow, pink or brown; vitreous; biaxial (+); Zeolite group. The September 2026 IMA-CNMNC Master List row reads Ba2(Si12Al4)O32·12H2O, status A, 1997 s.p., Germany.
- The barium-majority check. Coombs et al., the IMA zeolite report, Canadian Mineralogist 35 (1997) retain the name harmotome for the Ba-dominant member of the phillipsite series. Worked to 16 tetrahedral (Si + Al) sites, the sheet’s St. Andreasberg analysis gives 1.86 Ba and 0.62 K, and its Strontian analysis 1.88 Ba, 0.30 K and 0.50 Na. Barium is 0.75 and 0.70 of the extra-framework cation atoms, so both are harmotome by the rule.
- Four aluminium, two barium. By script over the IMA list, harmotome is the only row with (Si12Al4)O32, and the three phillipsite rows all carry (Si10Al6)O32·12H2O. Four aluminium need four positive charges, two barium; six need K6, Na6 or Ca3. Same framework count, different charge.
- Documented failure: the 2.448 line. The printed cell, 997.9 ų, with Z = 2 of the sheet’s ideal BaSi6Al2O16·6H2O gives 2.409, not the printed calculated density 2.448; the two analyses, recast, give 2.363 and 2.378. The measured 2.41–2.47 contains the ideal figure. This page could not reproduce 2.448 and does not use it.
- Where it is found. The sheet’s Distribution opens in Germany (St. Andreasberg, Harz Mountains; Idar-Oberstein; the Silberberg near Bodenmais), and lists fine crystals from Strontian, Argyllshire, Scotland, among others; strontianite and barite are on its association line. Barium-mineral hazard questions are routed to toxic minerals in a collection; nothing here is health or safety advice.
| Formula or analysis | Source | Ba | K | Na | Ca | Al per 16 T | Cation charge | Ba share | Name by the rule |
|---|---|---|---|---|---|---|---|---|---|
| Ba2(Si12Al4)O32·12H2O | IMA harmotome row | 2 | 0 | 0 | 0 | 4 | 4 | 1.00 | Harmotome |
| St. Andreasberg, Germany | Sheet analysis (1), recast | 1.86 | 0.62 | trace | Not printed | 4.55 | 4.34 | 0.75 | Harmotome |
| Strontian, Scotland | Sheet analysis (2), recast | 1.88 | 0.30 | 0.50 | Not printed | 4.73 | 4.57 | 0.70 | Harmotome |
| Andreasberg, Harz | Coombs et al. 1997, structure formula | 1.93 | 0.07 | Not printed | 0.46 | 4.66 | 4.85 | 0.79 | Harmotome |
| K6(Si10Al6)O32·12H2O | IMA phillipsite-K row | 0 | 6 | 0 | 0 | 6 | 6 | 0 | Phillipsite-K |
| Na6(Si10Al6)O32·12H2O | IMA phillipsite-Na row | 0 | 0 | 6 | 0 | 6 | 6 | 0 | Phillipsite-Na |
| Ca3(Si10Al6)O32·12H2O | IMA phillipsite-Ca row | 0 | 0 | 0 | 3 | 6 | 6 | 0 | Phillipsite-Ca |
What is harmotome? A barium zeolite of the phillipsite series
Harmotome is Ba2(Si12Al4)O32·12H2O, a monoclinic zeolite in which barium is the main cation between the framework’s tetrahedra. The Handbook of Mineralogy harmotome sheet heads it (Ba,K)1–2(Si,Al)8O16·6H2O and describes crystals elongated ∥ [001] or tabular ∥ {010}, typically striated on {010} ∥ [001], commonly as interpenetrant twins to 4 cm, alone, in groups or in radiating aggregates. Cleavage is distinct on {010} and poor on {001}; the fracture is uneven to subconchoidal; it is brittle, hardness 4.5, density 2.41–2.47. Colour runs from colourless and white through gray, yellow and pink to brown, with a white streak and vitreous lustre.
What the lists record. The September 2026 IMA-CNMNC Master List writes Ba2(Si12Al4)O32·12H2O, status A, 1997 s.p., country Germany. The sheet’s Mineral Group line reads Zeolite group, and Coombs et al. (1997) list harmotome among the accepted zeolites with framework code PHI, the phillipsite code. Its occurrence is of hydrothermal origin, in cavities in basalts, phonolites and trachytes, in gneisses, and in some ore veins. Type material is at the Natural History Museum, Paris; the sheet marks no type locality, so this page names none (what a type locality is).
The composition, worked. On standard atomic weights the IMA formula weighs 1447.76 g/mol, of which barium is 18.97%. As oxides it is SiO2 49.80, Al2O3 14.09, BaO 21.18 and H2O 14.93%, which is exactly the ideal column the sheet prints for BaSi6Al2O16·6H2O, half the IMA formula. The general zeolite question is on which minerals are zeolites.
Harmotome or phillipsite? The barium-majority check
Barium decides it: harmotome is the phillipsite-series zeolite in which barium is the most abundant extra-framework cation. Coombs et al., the IMA zeolite report, Canadian Mineralogist 35 (1997) name the members of a zeolite series by the extra-framework element most abundant in atomic proportions, and make an exception on grounds of history and usage: the name harmotome is retained for the Ba-dominant member of the phillipsite series. Their entry adds that harmotome forms a continuous series with phillipsite-Ca, and that the name harmotome predates phillipsite.
The check, worked on the sheet. Recast to 16 tetrahedral sites, the St. Andreasberg analysis (BaO 20.08, K2O 2.07, Na2O trace) gives 1.86 Ba and 0.62 K; barium is 0.75 of the cation atoms. The Strontian analysis (BaO 20.25, K2O 1.00, Na2O 1.09) gives 1.88 Ba, 0.30 K and 0.50 Na; barium is 0.70. Coombs et al.’s structure formula for Andreasberg, (Ba1.93Ca0.46K0.07)[Al4.66Si11.29O32]·12H2O, gives 0.79. All three are harmotome by the rule. The IMA rows for phillipsite carry no barium at all: K6, Na6 and Ca3 on (Si10Al6)O32·12H2O.
Documented failure: the charge does not quite close. On the IMA formula two barium balance four aluminium exactly. On the sheet’s analyses the cation charge, 2Ba + K + Na, is 4.34 against 4.55 Al (St. Andreasberg) and 4.57 against 4.73 (Strontian), about 0.2 short in each, and the water, 10.24 and 10.64 H2O per 16 tetrahedra, sits below the IMA 12. The analyses also carry more aluminium than the IMA formula: silicon is 0.716 (St. Andreasberg) and 0.704 (Strontian) of the tetrahedral sites against the formula’s 0.750. Coombs et al. print 0.68–0.71 for harmotome: the Strontian analysis falls inside it, St. Andreasberg just above it, and the IMA formula outside. The rule needs an analysis; it is not a hand test, and the zeolite comparisons on is chabazite a zeolite and is thomsonite a zeolite are built the same way for their own species.
Harmotome twins: what the sheet records
The sheet records interpenetrant twins, repeated on {001}, {021} and {110}, and says three double twins may further twin to simulate a pseudotetragonal prism or dodecahedron. That is the habit behind the name: the sheet derives harmotome from the Greek harmos, for a joint, and tome, for a cutting, as the twinned crystals may be divided, and Coombs et al. (1997) give the same derivation, in allusion to a tendency to split along junctions, the twin planes. The harmotome sheet does not use the word cruciform; the Handbook’s phillipsite sheet does, for its own cruciform single and double penetration twins, so this page does not apply it to harmotome.
Documented failure: the 2.448 line. The sheet prints a calculated density of 2.448. The printed cell, a = 9.8688, b = 14.1295, c = 8.7092 Å, β = 124.74°, holds 997.9 ų. Two formula units of the sheet’s own ideal BaSi6Al2O16·6H2O, 723.88 g/mol, give 2 × 723.88 ÷ (0.60221 × 997.9) = 2.409. Recast with their potassium, sodium and lower water, the St. Andreasberg and Strontian analyses give 2.363 and 2.378. None reaches 2.448. The measured range, 2.41–2.47, contains the ideal figure, and this page quotes the measured range.
On the balance. At density 2.41–2.47 a 20.00 g piece reads 11.70–11.90 g in water; the phillipsite sheet’s 2.20 gives 10.91 g. The method is on how to measure specific gravity at home. Hardness 4.5 is the top of the phillipsite sheet’s 4–4.5, so hardness does not separate them (how to test mineral hardness properly).
Where is harmotome found? Strontian, the Harz and elsewhere
The harmotome sheet’s Distribution, as printed. Many occurrences; some for well-studied material: in Germany, from St. Andreasberg, Harz Mountains; at Idar-Oberstein, Rhineland-Palatinate; and on the Silberberg, near Bodenmais, Bavaria. At Příbram, Czech Republic. From Sarrabus, Sardinia, Italy. Fine crystals from Strontian, Argyllshire, Scotland. From Kongsberg, Norway. At Kupferberg-Rudelstadt, Silesia, Poland. In the Korsnäs lead mine, south of Vaasa, Finland, the source of the X-ray pattern. In Russia, large crystals at Bukan, in the Kotuy River basin, Taimyr. In the USA, from Glen Riddle, Delaware Co., Pennsylvania, and at Sing Sing, near Ossining, Westchester Co., New York. In the Beaver mine, Thunder Bay district, Ontario, Canada. At Batopilas, Chihuahua, Mexico. We add no other locality.
Strontian. The sheet prints fine crystals from Strontian and one of its two analyses is Strontian material. Its association line names zeolites, calcite, leucite, hyalophane, strontianite, quartz, kaolinite, barite, pyrite, sphalerite and galena. Other barium minerals on this site are baryte and witherite.
Barium-mineral hazard questions are routed to toxic minerals in a collection; nothing here is health or safety advice. More species are in the species index. We hold no catalogue and nothing here is offered for sale; the wanted list is the only commercial route.