Is cavansite a zeolite?
Not by the 1997 IMA test: cavansite’s silicate layers are joined by vanadyl pyramids, not tetrahedra. Evans (1973) called its water zeolitic. Hardness 3 to 4.
Not by the IMA definition, though its water is called zeolitic. Coombs et al. (1997) define a zeolite by a framework of linked tetrahedra; Evans (1973) found cavansite’s silicate layers joined by square-pyramidal vanadyl groups instead. The 1997 report never names cavansite, Ca(V4+O)(Si4O10)(H2O)4, hardness 3 to 4, which grows with zeolites in basalt and tuff.
In short
- The definition. The IMA zeolite report (Coombs et al. 1997) defines a zeolite mineral by a structure characterized by a framework of linked tetrahedra, each consisting of four O atoms surrounding a cation, with open cavities in the form of channels and cages, dehydrating mostly below about 400 °C, largely reversibly. The framework may be interrupted by (OH,F) groups. Cavansite is not mentioned in the report, by script.
- The structure. Evans (1973), American Mineralogist 58, 412–424 found cavansite to be a novel layer-silicate structure: SiO4 tetrahedra in sheets, with vanadium in square-pyramid coordination and calcium in 7-fold coordination between the layers. The vanadyl groups join the layers into a three-dimensional framework with large channels, and Evans calls both cavansite and its dimorph pentagonite certainly zeolitic in character.
- The gismondine subtraction. Evans’s own comparison: remove the VO2+ groups, join the facing tetrahedral apices directly (subtracting VO3), replace half the Si by Al, and the result is the framework of the zeolite gismondine, CaAl2Si2O8·4H2O. Worked: Ca V Si4 O11·4H2O − V O3 = Ca Si4 O8·4H2O, whose cations total +18 against 16 negative charges; swapping 2 Si for 2 Al brings it to +16. Doubled, that is the IMA’s gismondine-Ca, Ca2(Si4Al4)O16·8H2O.
- The group-line check. The cavansite sheet names 10 associates across Oregon and India. Of their sheets, 5 print Zeolite group: heulandite, stilbite, analcime, thomsonite and mordenite. The cavansite and pentagonite sheets print no Mineral Group line, and the IMA list has no group column. Cavansite grows on zeolites; neither its sheet nor the 1997 report files it with them.
- The decision. On a label, cavansite is a calcium vanadium silicate, not a zeolite; “zeolitic” is fair for its water, attributed to Evans. The species page is cavansite; the dimorph question is on pentagonite vs cavansite. Other near-zeolites: is okenite a zeolite, is apophyllite a zeolite, is prehnite a zeolite.
| Name | Formula (IMA), status | Mineral Group line (sheet) | Mentions in the 1997 zeolite report | What links the framework (source) |
|---|---|---|---|---|
| Cavansite | Ca(V4+O)(Si4O10)(H2O)4; A, 1967-019 | None printed | 0 | Silicate layers joined by square-pyramidal vanadyl groups (Evans 1973) |
| Pentagonite (dimorph) | CaV4+OSi4O10(H2O)3·H2O; A, 1971-039 | None printed | 0 | As cavansite, with 6-fold rings (Evans 1973) |
| Gismondine (comparison) | Ca2(Si4Al4)O16·8H2O, as gismondine-Ca; Rn, 1997 s.p. | Zeolite group | 18 | Tetrahedral layers linked directly into a three-dimensional aluminosilicate network (Evans 1973) |
| Heulandite | (Ca,Na,K)5(Si27Al9)O72·26H2O, as heulandite-Ca; Rn, 1997 s.p. | Zeolite group | 46 | Zeolite series in the report |
| Stilbite | NaCa4(Si27Al9)O72·28H2O, as stilbite-Ca; A, 1997 s.p. | Zeolite group | 57 | Zeolite series in the report |
| Analcime | Na(AlSi2O6)·H2O; A, 1997 s.p. | Zeolite group | 55 | Zeolite in the report |
| Thomsonite | NaCa2(Al5Si5)O20·6H2O, as thomsonite-Ca; Rn, 1997 s.p. | Zeolite group | 29 | Zeolite in the report |
| Mordenite | (Na2,Ca,K2)4(Al8Si40)O96·28H2O; A, 1997 s.p. | Zeolite group | 27 | Zeolite in the report |
| Apophyllite | KCa4(Si8O20)F(H2O)8, as fluorapophyllite-(K); Rn, 1978 s.p. | None printed | 0 | Not stated here; see the apophyllite page |
| Calcite | Ca(CO3); G, 1836 | Calcite group | — | Not a silicate |
| Copper | Cu; G | None printed | — | Native element |
| Chalcocite | Cu2S; G, 1751 | None printed | — | Sulfide |
Is cavansite a zeolite? What the IMA definition requires
A zeolite, on the IMA’s 1997 definition, is built on a framework of linked tetrahedra. The IMA zeolite report (Coombs et al. 1997) reads: a zeolite mineral is a crystalline substance with a structure characterized by a framework of linked tetrahedra, each consisting of four O atoms surrounding a cation. This framework contains open cavities in the form of channels and cages, usually occupied by H2O molecules and extra-framework cations that are commonly exchangeable; the channels are large enough to allow the passage of guest species; in hydrated phases, dehydration occurs at temperatures mostly below about 400 °C and is largely reversible. The framework may be interrupted by (OH,F) groups occupying a tetrahedron apex that is not shared.
What the definition does allow. The report accepts elements other than Si and Al in the tetrahedra: the beryllosilicates lovdarite and chiavennite, the zincosilicate gaultite, and the beryllophosphates pahasapaite and weinebeneite, which have neither Si nor Al. What the definition keeps fixed is the tetrahedron itself. The report names cavansite 0 times and pentagonite 0 times, by script; its only vanadium words are in one line equating vanadio-laumontite with vanadian laumontite.
What cavansite is. The Handbook of Mineralogy cavansite sheet gives Ca(V4+O)Si4O10·4H2O, orthorhombic, prismatic crystals to 1 mm and spherulitic rosettes to 5 mm, hardness 3 to 4, density 2.21 to 2.31, brilliant sky-blue to greenish blue, and prints no Mineral Group line. The September 2026 IMA list writes Ca(V4+O)(Si4O10)(H2O)4, status A, IMA 1967-019, USA.
Why cavansite is not a zeolite: the gismondine subtraction
Cavansite’s framework is closed by vanadium pyramids, not by tetrahedra. Evans (1973), American Mineralogist 58, 412–424 describes SiO4 tetrahedra with three corners shared with other tetrahedra and the fourth coordinated to one V and one Ca atom; VO2+ groups coordinated to the apices of 4 SiO4 tetrahedra, so that V is in square-pyramidal coordination; and Ca2+ in 7-fold coordination. The silicate tetrahedra form layers; the vanadyl groups join the layers into three-dimensional frameworks with large channels parallel to the c axis.
Evans’s own comparison, worked. Evans writes that if the VO2+ groups are removed and the opposite tetrahedral apices joined directly, subtracting VO3, and half the Si atoms are replaced by Al, a framework identical topologically with that of the zeolite gismondine, CaAl2Si2O8·4H2O, is obtained. In atoms: Ca V Si4 O11·4H2O minus V O3 leaves Ca Si4 O8·4H2O; its cations carry +18 against 16 negative charges on eight oxygens, and replacing 2 of the 4 Si with Al brings them to +16. Doubled, Ca2Al4Si4O16·8H2O is the IMA’s gismondine-Ca, Ca2(Si4Al4)O16·8H2O.
What the subtraction measures. It takes one vanadium and three oxygens out of every formula unit, and a change of half the silicon, to turn cavansite’s linkage into a zeolite’s. Evans puts the difference in one sentence: in gismondine the exposed tetrahedral apices in adjacent layers are linked, not through VO2+ groups, but directly, to form a three-dimensional aluminosilicate network. On the 1997 definition, that direct tetrahedral linkage is the requirement.
Why is cavansite called zeolitic? Evans’s water, and a documented failure
Because its water behaves like a zeolite’s, as far as anyone had looked in 1973. Evans writes that although no physical chemical studies had been made on cavansite and pentagonite, both are certainly zeolitic in character: the vanadyl groups join the layers into frameworks with large channels, and in cavansite 8-fold ring openings would allow zeolitic migration in three dimensions, hardly more than one in pentagonite. Staples, Evans and Lindsay (1973), American Mineralogist 58, 405–411 attribute the small variation in the cell dimensions, presumably, to varying zeolitic water content. No fetched source here measures a dehydration temperature, so this page cannot test the definition’s 400 °C clause.
Documented failure: the water was first got wrong. Staples and colleagues found Ca, V and Si in the mole ratios 1 : 1 : 4 by X-ray fluorescence but could not determine the water by their usual methods; an estimated 21.0% suggested n = 6. Worked from the sheet’s cell, n = 6 gives a density of 2.517, the 2.52 Staples printed, far above the measured 2.31; n = 4 gives 2.331, the sheet’s 2.33. The structure analysis fixed the formula at four waters, 15.96% H2O, and the Handbook’s first analysis column still carries the bracketed [21.0].
What that changes. Zeolitic water is one of the characteristic features the report lists, but it is not the definition. Okenite and apophyllite also grow with zeolites and carry water, and are not zeolites either; their cases are set out on is okenite a zeolite and is apophyllite a zeolite.
Cavansite on zeolites: the group-line check
Cavansite sits on zeolites, and its own sheet does not file it with them. Method: the cavansite sheet’s Association line names pentagonite, calcite, heulandite, stilbite, analcime, apophyllite, thomsonite and copper in Oregon, and stilbite, calcite, heulandite, mordenite and chalcocite in India: 10 distinct names. Each was represented by a Handbook sheet and its Mineral Group line read by script. 5 print Zeolite group: heulandite, stilbite, analcime, thomsonite and mordenite. Calcite prints Calcite group; pentagonite, apophyllite, copper and chalcocite print none; so does cavansite.
In the 1997 report. The five zeolite associates are mentioned 27 to 57 times each, by the same script, and gismondine 18 times; cavansite and pentagonite 0. Those counts are positive controls: the script finds the zeolites the report treats, and not cavansite. How the series work is on is chabazite a zeolite and is thomsonite a zeolite; the zeolite family is on which minerals are zeolites.
Where it is found. The sheet names the Owyhee Dam area, Lake Owyhee State Park, Malheur Co., and the Chapman quarry, Columbia Co., Oregon, and remarkable specimens from quarries around Wagholi, Poona district, Maharashtra, India: in tuff, vesicular basalt and altered basalt breccia, as cavity fillings. Its crystals reach 1 mm, the scale on what is a micromount. The species page is cavansite; the rest is indexed at the collecting guides. Nothing on this site is offered for sale; the wanted list is the only commercial route.