Natrolite
Natrolite is Na2Al2Si3O10·2H2O: hardness 5 to 5.5, density 2.20 to 2.26, prisms to 1 m, commonly fluorescent orange to yellow. 20 old-name entries mean it.
Natrolite is the sodium zeolite Na2Al2Si3O10·2H2O: orthorhombic prisms to 1 m and radiating sprays in basalt cavities, hardness 5 to 5.5, measured density 2.20 to 2.26, perfect {110} cleavage, and on its Handbook sheet it commonly fluoresces orange to yellow under UV. The 1997 IMA zeolite report equates 20 entries in its obsolete-names list outright with natrolite.
In short
- Two formulas, one mineral. The September 2026 IMA-CNMNC Master List writes Na2(Si3Al2)O10·2H2O, status A, 1997 special procedure, Germany; the Handbook of Mineralogy sheet writes Na2Al2Si3O10·2H2O. The IMA row brackets the silicon and aluminium, the tetrahedral framework atoms, which the 1997 zeolite report writes as [Al2Si3O10]; the atoms are the same. Worked on standard atomic weights: 16.30% Na2O and 9.48% water by mass.
- The old-label decoder. The 1997 IMA zeolite report lists 193 obsolete and discredited names with their modern equivalents. A script over that list finds 20 entries equated outright with natrolite, from bergmannite and brevicite to galactite and savite, and 10 more that name natrolite with a qualifier or alongside other species such as mesolite, scolecite or thomsonite.
- Three traps with natro in the name. Natrochabazite and natron-chabasit are gmelinite, and pseudonatrolite is mordenite, per the same list. An old label containing the letters natro is not evidence of natrolite.
- Weight will not pick it out. A 20.00 g piece reads 10.91 to 11.15 g in water; mesolite 11.15 g, scolecite 11.11 to 11.27 g, gonnardite 11.11 to 11.53 g. All four overlap. The sheet even warns its X-ray powder pattern may be confused with gonnardite’s.
- Where. The sheet names the Dean quarry, St. Keverne, Cornwall, and White Head, Co. Antrim, among many; large crystals from the Khibiny and Lovozero massifs; huge crystals from the Johnston asbestos mine, near Thetford, Quebec; and the Gem mine, San Benito Co., California, see the Benitoite Gem Mine.
| Species | IMA formula | IMA status, year | Na2O by mass, worked | Water by mass, worked | Hardness | Density (measured) | 20.00 g piece in water | UV on the sheet |
|---|---|---|---|---|---|---|---|---|
| Natrolite | Na2(Si3Al2)O10·2H2O | A, 1997 s.p. | 16.30% | 9.48% | 5 to 5.5 | 2.20 to 2.26 | 10.91 to 11.15 g | Commonly fluoresces orange to yellow |
| Paranatrolite | Na2(Si3Al2)O10·3H2O | A, 1978-017 | 15.56% | 13.57% | 5 to 5.5 | 2.21 to 2.29 | 10.95 to 11.27 g | None printed |
| Gonnardite | (Na,Ca)2(Si,Al)5O10·3H2O | Rd, 1997 s.p. | 7.67% (Handbook formula Na2CaAl4Si6O20·7H2O) | 15.60% (Handbook formula) | 5 | 2.25 to 2.36 | 11.11 to 11.53 g | None printed |
| Mesolite | Na2Ca2(Si9Al6)O30·8H2O | A, 1997 s.p. | 5.32% | 12.37% | 5 | 2.26 | 11.15 g | None printed |
| Scolecite | Ca(Si3Al2)O10·3H2O | A, 1997 s.p. | 0% | 13.78% | 5 to 5.5 | 2.25 to 2.29 | 11.11 to 11.27 g | May fluoresce yellow to brown, SW and LW |
What is natrolite? The sodium member of the NAT family
The definition. Natrolite is a zeolite: the Coombs et al. 1997, Recommended nomenclature for zeolite minerals (Canadian Mineralogist 35) lists it as Na2[Al2Si3O10]•2H2O with the framework code NAT, and says that natrolite, mesolite and scolecite have the same topologically distinctive framework and compositions that are distinctive, so each is a separate species. The September 2026 IMA-CNMNC Master List gives Na2(Si3Al2)O10·2H2O, status A, 1997 special procedure, Germany. The Handbook sheet gives Na2Al2Si3O10·2H2O, Zeolite group, and the name from the Latin natron, for the sodium content. Why the zeolites are defined by structure rather than by water is on which minerals are zeolites.
What it looks like. Orthorhombic, pseudotetragonal. Crystals are short to long prismatic, to 1 m, commonly {110} terminated by {111} and striated along the length; in stellate or interlacing groups; also radiating fibrous, granular, or compact and massive. Twinning on {110}, {011} and {031}. Cleavage {110} perfect, parting on {010}, fracture uneven, brittle. Colourless, white, grey, bluish, yellowish or pink, vitreous to pearly. Biaxial positive, α 1.473 to 1.483, γ 1.485 to 1.496. The sheet also records it as pyroelectric and piezoelectric.
The sodium check, worked. On standard atomic weights the formula mass is 380.22: 16.30% Na2O, 26.82% Al2O3, 47.41% SiO2 and 9.48% H2O. The sheet’s analysis, from Puy de Marman, France, gives 15.36% Na2O, 0.94 points short, and recalculates to Na 1.88 with K 0.02 and Ca 0.01 per three silicon, as the sheet itself prints. In the family table, only paranatrolite comes close on sodium, at 15.56%; mesolite is 5.32% and scolecite has none. That is a laboratory distinction, not a hand test.
Is my old natrolite label right? The old-label decoder
Method. The 1997 IMA zeolite report includes a list of obsolete and discredited names, based on one compiled by G. Gottardi from Hintze, Dana, Hey, Strunz and others, each followed by its correct name or identification. The list was read from the fetched PDF (pdftotext -layout) and parsed by script, two columns and wrapped lines handled: 193 entries. Of those, 30 name natrolite on the right-hand side.
Twenty equate a name outright with natrolite: aedelite (of Kirwan) and aedilite, apoanalcite, bergmannite, brevicite, crocalite, echellite, epinatrolite, fargite, galactite, hegauit and högauite (two entries), hydronatrolite, krokalith, laubanite, lehuntite, mooraboolite, portite (with a 1994 citation), radiolite (of Esmark), savite and soda mesotype. Ten more name it with a qualifier or among others: natronite (in part), spreustein (mostly), metanatrolite (partially dehydrated natrolite), eisennatrolith (natrolite with other mineral inclusions), ellagite (a ferriferous natrolite or scolecite?), hydronephelite (a mixture, probably containing natrolite), doranite (analcime with thomsonite, natrolite and Mg-rich clay minerals), hairzeolite (natrolite, thomsonite, mordenite), and mesotype and needle zeolite or needle stone (natrolite, mesolite, scolecite).
The rule, and its traps. An old label from the first group can be read as natrolite; one from the second group is a reason to re-examine the piece, because mesotype and needle stone covered three species that hardness and weight cannot separate. Three entries carry the letters natro and are not natrolite: natrochabazite and natron-chabasit (of Naumann) are gmelinite, and pseudonatrolite is mordenite. The other old-name questions on this site are is apophyllite a zeolite and is prehnite a zeolite, and what a type locality is, for older labels that cite one, is on what is a type locality.
Natrolite, mesolite or scolecite? What weight and UV can and cannot do
Documented failure: the balance. Worked as 20 − 20/D from the measured densities, a 20.00 g piece of natrolite reads 10.91 to 11.15 g in water. Mesolite reads 11.15 g, scolecite 11.11 to 11.27 g, gonnardite 11.11 to 11.53 g, paranatrolite 10.95 to 11.27 g. Every range overlaps natrolite’s, so the method on how to measure specific gravity at home confirms a zeolite-weight mineral and stops there. The hardness ranges, 5 to 5.5 against 5, overlap too.
The habit and twin evidence is set out on the scolecite page, with the mesolite arithmetic, and the optical evidence on mesolite; neither is repeated here. Paranatrolite, on its own Handbook sheet, occurs as radial fibrous aggregates to 5 mm and as epitaxial overgrowths on natrolite. The 1997 report put paranatrolite among zeolites of doubtful status and says it dehydrates to tetranatrolite; the natrolite sheet calls natrolite dimorphous with tetranatrolite, and the September 2026 IMA list has no row named tetranatrolite, searched by script.
UV is a pointer. A ligature-aware search of the five family sheets (the text extraction prints the fl of fluoresces as a stray glyph; the hemimorphite and willemite sheets were the positive controls) finds two with UV wording: natrolite, commonly fluoresces orange to yellow under UV, and scolecite, may fluoresce yellow to brown under SW and LW UV. Mesolite, gonnardite and paranatrolite print none, which is a blank field, not a measured absence. The lamp question in general is on fluorescent minerals explained.
Where natrolite is found: Cornwall, Antrim, Kola and Quebec
The Distribution field begins many localities, even for fine crystals, then names: the Höwenegg quarry, Hegau, Baden-Württemberg, Germany; Puy de Marman, near Veyre, Puy-de-Dôme, France; the Dean quarry, St. Keverne, Lizard Peninsula, Cornwall; White Head, Co. Antrim, Ireland; the Langesundsfjord and Tvedalen areas, Norway; large crystals in the Khibiny and Lovozero massifs, Kola Peninsula, Russia.
In North America, per the sheet: Bergen Hill, Prospect Park and the Chimney Rock quarry, New Jersey; north of Livingstone, Montana; around Springfield, Oregon; the Gem mine, San Benito Co., California, which the benitoite sheet also names, describing benitoite there in natrolite veins cutting glaucophane schist, with natrolite among its associates (the locality is on the Benitoite Gem Mine page); huge crystals from the Johnston asbestos mine near Thetford, and Mont Saint-Hilaire, Quebec; the Bay of Fundy district, Nova Scotia; and the Ice River, British Columbia.
Its setting. The sheet places natrolite in cavities in amygdaloidal basalts and related igneous rocks, one of the last minerals to form, and in seams in granite, gneiss and syenite, with zeolites, calcite, nepheline, sodalite and quartz. The other zeolites with pages here include analcime, stilbite and heulandite; the rest of the reference section is at the species index. We hold no catalogue and nothing here is offered for sale; the wanted list is the only commercial route.