Is Okenite a Zeolite?
No. Okenite, Ca10Si18O46(H2O)18, keeps its silicon in tetrahedral sheets and chains, not the open framework the IMA zeolite report needs. Found with prehnite.
No. The 1997 IMA zeolite report defines a zeolite by a framework of linked tetrahedra with open channels and cages, and never mentions okenite. Merlino’s 1983 structure puts okenite’s 18 silicon atoms in two tetrahedral sheets (12) and one double chain (6), none in a framework. Okenite, Ca10Si18O46(H2O)18, density 2.28 to 2.33, grows with zeolites in basalt.
In short
- The definition. Coombs et al. 1997, the IMA zeolite report defines a zeolite as a crystalline substance with a framework of linked tetrahedra, each of four O atoms around a cation, containing open cavities in the form of channels and cages. A script counts 0 occurrences of okenite in the report, against 72 of natrolite.
- The 12–6–0 ledger. Merlino 1983, American Mineralogist 68, 614–622 solved the structure as tetrahedral sheets (Si6O15), double chains (Si6O16) made by pairing two wollastonite chains, and octahedral double chains, joined into layers that alternate with calcium–water sheets. Per Ca10Si18O46·18H2O: 12 silicon atoms in sheets, 6 in a chain, 0 in a framework.
- Documented failure: water and weight. Merlino reports thermal-analysis peaks at 100, 190 and 370 °C (Phadke and Kshirsagar 1980), all inside the report’s “mostly below about 400°C” for zeolite dehydration. A 20.00 g piece reads 11.23 to 11.42 g in water, overlapping scolecite and thomsonite-Ca. Neither test excludes it; the structure does.
- The cotton-ball check. Okenite’s sheet gives compact radial fibrous balls to 4 cm with an elastic tenacity; the natrolite, mesolite, scolecite and thomsonite-Ca sheets all print brittle. The table below sets out eight white fibrous or radiating minerals from basalt cavities.
- Not repeated here. Water by mass is on which minerals are zeolites; the oxygen-count test on is prehnite a zeolite; whether okenite counts as asbestos on is scolecite asbestos.
| Mineral | IMA formula | Zeolite? (1997 report mentions; sheet group line) | Habit (sheet) | Tenacity (sheet) | Hardness | Density | 20.00 g in water |
|---|---|---|---|---|---|---|---|
| Okenite | Ca10Si18O46(H2O)18 | No: 0; no group line | Bladed crystals or laths, typically fibrous; compact radial fibrous balls, to 4 cm | Elastic | Printed “.5–5”; not quoted | 2.28–2.33 | 11.23–11.42 g |
| Nekoite | Ca3Si6O15(H2O)5·2H2O | No: 0; no group line | Fine, slender needles, to 5 mm | n.p. | n.d. | 2.21–2.24 | 10.95–11.07 g |
| Mesolite | Na2Ca2(Si9Al6)O30·8H2O | Yes: 20; Zeolite group | Hairlike tufts and aggregates of fibres; divergent, radiating compact masses | Brittle, but compact masses are tough | 5 | 2.26 | 11.15 g |
| Natrolite | Na2(Si3Al2)O10·2H2O | Yes: 72; Zeolite group | Stellate or interlacing groups; radiating fibrous | Brittle | 5–5.5 | 2.20–2.26 | 10.91–11.15 g |
| Scolecite | Ca(Si3Al2)O10·3H2O | Yes: 18; Zeolite group | Radiating sprays, fibrous masses | Brittle | 5–5.5 | 2.25–2.29 | 11.11–11.27 g |
| Thomsonite-Ca | NaCa2(Al5Si5)O20·6H2O | Yes: 29 (as thomsonite); Zeolite group | Radiated spherical or columnar aggregates; globular, botryoidal | Brittle | 5–5.5 | 2.23–2.39 | 11.03–11.63 g |
| Gyrolite | NaCa16(Si23Al)O60(OH)8(H2O)14 | No: 0; no group line | Spherical to radial masses, to 5 cm; platy or plumose | Flakes flexible | 3–4 | 2.388–2.390 | 11.62–11.63 g |
| Pectolite | NaCa2Si3O8(OH) | No: 0; no group line | Acicular, to 15 cm; radiating fibrous, spheroidal | Brittle; tough when compact | 4.5–5 | 2.84–2.90 | 12.96–13.10 g |
Is okenite a zeolite? What the IMA definition requires
Okenite is not a zeolite: the IMA definition requires a framework of linked tetrahedra with open channels and cages, and okenite has none. Coombs et al. 1997, the IMA zeolite report write that 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; the framework contains open cavities in the form of channels and cages, usually occupied by H2O molecules and extra-framework cations that are commonly exchangeable. Okenite does not appear anywhere in the report: a case-insensitive count over its text finds 0, where natrolite returns 72.
What okenite is. The September 2026 IMA list writes Ca10Si18O46(H2O)18, grandfathered, 1828, with Denmark (Greenland) as the country of first description. The Handbook of Mineralogy okenite sheet writes Ca5Si9O23·9H2O, the same ratios halved, and prints no group line: triclinic, bladed crystals or laths, typically fibrous, in compact radial fibrous balls to 4 cm, perfect {001} cleavage, elastic, density 2.28 to 2.33.
Why the question gets asked. The sheet places okenite commonly in amygdules in basalts and lists zeolites first among its associates, with apophyllite, prehnite, calcite, quartz and chalcedony. Merlino 1983, American Mineralogist 68, 614–622 opens by noting that okenite’s consistent association with gyrolite and zeolites in basalts seemed indicative of some structural relations among them. It was the structure that answered that.
What is okenite’s structure? The 12–6–0 ledger
The 12–6–0 ledger: of okenite’s 18 silicon atoms per formula, 12 are in tetrahedral sheets, 6 in a double chain and 0 in a framework. Merlino solved the structure on a crystal from Kolhapur District, Maharashtra, and wrote it as [Ca8(Si6O16)(Si6O15)2(H2O)6]−4 [Ca2(H2O)9·3H2O]+4. The units are tetrahedral sheets S, (Si6O15)−6, with five- and eight-membered rings; three-repeat double chains C, (Si6O16)−8, made by pairing two wollastonite chains; and octahedral double chains O. They join by corner sharing into complex layers SOCOS, which alternate with calcium–water sheets. Two sheets and one chain: 12 + 6 = 18 silicon atoms and 30 + 16 = 46 oxygens, the IMA formula exactly.
Where that sits among silicates. Merlino cites Zoltai’s 1960 classification of tetrahedral structures by how far they extend: isolated groups, chains and rings, sheets, frameworks, and a fifth, mixed type. He calls okenite the first example of a silicate with both tetrahedral chains and sheets, and in 1983 the only known member of that mixed class. The 1997 definition asks for a framework, Zoltai’s three-dimensional class. The same reasoning for apophyllite is on is apophyllite a zeolite.
What would change the answer. The report accepts interrupted frameworks, where an (OH) group or F atom takes a tetrahedron apex not shared with its neighbour, so a few unshared corners alone would not rule a mineral out. Okenite’s case is different in kind: Merlino’s sheets and chains join into layers, not into a three-dimensional framework. The report also sets aside how industry uses the word for synthetic materials; this page uses the mineralogical sense only.
Okenite or a zeolite? The cotton-ball check
Okenite’s white fibrous balls are recorded as elastic; the fibrous zeolites they grow with are recorded as brittle. On their Handbook sheets, natrolite, scolecite and thomsonite-Ca print brittle, and mesolite brittle, but compact masses are tough. Okenite’s sheet prints elastic, gyrolite’s flakes flexible. Habit points the same way: okenite’s bladed laths and compact radial balls against mesolite’s hairlike tufts and natrolite’s stellate groups. The natrolite–scolecite separation is on natrolite vs scolecite and not repeated here.
Documented failure: weight. A 20.00 g piece of okenite reads 11.23 to 11.42 g in water. Scolecite reads 11.11 to 11.27 g and thomsonite-Ca 11.03 to 11.63 g, both overlapping it, and mesolite’s 11.15 g is 0.08 g below, so the balance does not decide it. pectolite, at 12.96 to 13.10 g, is more than 1.5 g away. Method: how to measure specific gravity at home.
Documented failure: water. The 1997 report says zeolite dehydration occurs mostly below about 400 °C and is largely reversible. Merlino reports thermal-analysis peaks at 100, 190 and 370 °C from Phadke and Kshirsagar (1980), which he correlates with three kinds of structural water. On temperature alone okenite would pass. And the sheet records that nekoite, named as an anagram of okenite, was originally mistaken for it. The water-by-mass comparison is on which minerals are zeolites.
Is okenite asbestos, and where is it found?
Whether okenite counts as asbestos is answered on is scolecite asbestos, which checks it against the regulation’s named list; nothing on this page is health, safety or legal advice. The okenite sheet records the habit as typically fibrous; a habit is not a legal classification.
Where the sheet places it. Qutdligssat (Kudlisat) and Disko Island, Greenland; Bordoy and Streymoy, Faeroe Islands; Scawt Hill, near Larne, Co. Antrim; the Isle of Mull and Morven Peak, Scotland; in Maharashtra, India, the Syhadree Mountains, the Bombay quarry, around Poona, and the Nasik and Kolhapur districts; Rio Putagan, Chile; the Noche Buena mine, Zacatecas, Mexico; Crestmore, California, the Fairfax quarry, Virginia, and Skookumchuck Dam, Washington; and the Jeffrey mine, Asbestos, Quebec. The zeolite questions are indexed at the collecting guides, with is chabazite a zeolite and is thomsonite a zeolite for two that are. Nothing on this site is offered for sale; the wanted list is the only commercial route.