Eudialyte

What is eudialyte? The sheet’s description

Eudialyte is a sodium zirconium silicate of alkaline igneous rocks, hardness 5 to 6, density 2.74 to 3.10, usually red, pink or brown. The Handbook of Mineralogy eudialyte sheet gives a hexagonal mineral, point group 3̄ 2/m, space group R3̄m, forming short rhombohedral crystals with {0001} dominant, to long prismatic, up to 10 cm, and more commonly irregular masses and vein fillings. Cleavage is perfect to indistinct on {0001} and imperfect on {11-20}; the fracture is uneven and the mineral brittle. It is uniaxial, positive or negative, with ω 1.588 to 1.636 and ε 1.588 to 1.658.

Where it grows. The sheet places it in nepheline syenites, alkalic granites and associated pegmatites, where it may be a major constituent, of both magmatic and late-stage pneumatolytic origin. Its listed associates include microcline, nepheline, aegirine, lamprophyllite, lorenzenite, murmanite, arfvedsonite, sodalite, aenigmatite, rinkite, låvenite, titanite and titanian magnetite; nepheline, sodalite, microcline and titanite have their own pages.

By weight. On the sheet’s measured density, a clean 20.00 g piece reads 12.70 to 13.55 g in water (20 − 20/D); the method is on how to measure specific gravity at home. The range is wide because the composition is; weight alone does not separate eudialyte from the other group members.

Is eudialyte a group? The 17-to-32 ledger

Yes: eudialyte names one species and a whole group, and the group has nearly doubled since its nomenclature report. Johnsen et al. 2003, Canadian Mineralogist 41, 785–794, the report of the IMA eudialyte nomenclature subcommittee, describes the group as Na-rich zirconosilicates, trigonal, a ≈ 14 Å, c ≈ 30 Å (rarely 60 Å), with nine- and three-membered rings of silicate tetrahedra, and says the number of minerals in the group is approaching twenty. Its Table 1 lists 17. It recommends unique names with at most one cation prefix, referring to the M(2) site, as in ferrokentbrooksite.

Method. The IMA list has no group column, so the ledger is a formula scan, not a membership statement. A script parses every row of the September 2026 list, rejoins formulas that wrap onto two lines, and keeps rows whose formula contains zirconium and the eudialyte framework written any of the ways the list uses: Si(Si25O73), Si26O72, Si24O66, Si51O144 and the like, or Si9O27 rings. That rule finds 31 rows. A second rule, the same silicate with titanium or niobium and no zirconium or aluminium, adds alluaivite, which Johnsen et al. include. The 32 are tabled above. All 17 of the 2003 names are present; the other 15 were approved later.

Status, attributed. Johnsen et al. give eudialyte’s status as grandfather clause (Stromeyer 1819, Johnsen and Grice 1999); the 2026 IMA list records A, 2003 s.p., the year of the report. Documented failure: the report says an accurate formula can only be constructed from data based on structural information, and the Handbook sheet’s Kipawa Lake powder pattern carries the note could be mistaken for alluaivite. A label reading eudialyte on an unanalysed specimen should be read as eudialyte group.

Where eudialyte is found: the sheet’s localities

The sheet calls the localities numerous, a number affording fine crystals, and names these. In Greenland, on the Kangerdluarssuk Plateau, in the Ilímaussaq intrusion, at Narssârssuk and elsewhere. Around the Langesundsfjord, Norway. In Russia, the Lovozero and Khibiny massifs, Kola Peninsula; Barynga Ridge, Taimyr; and the Burpala massif, about 120 km north of Lake Baikal. In the USA, Magnet Cove, Hot Spring Co., Arkansas; Point of Rocks, Colfax Co., and a large deposit at Pajarito Mountain, Otero Co., New Mexico. In Canada, Seal Lake and the Red Wine complex, Labrador; the Sheffield Lake complex, Kipawa River, Villedieu Township; Mont Saint-Hilaire and near Saint-Amable, Quebec. Also Tenerife, Canary Islands.

First description. Johnsen et al. say eudialyte was first described from Kangerdluarssuk, in the Ilímaussaq alkaline complex, South Greenland (Stromeyer 1819); the IMA list gives the country as Denmark (Greenland). The sheet itself prints no type locality line, and this page adds none beyond those two sources.

Two analyses, two eudialytes: Kipawa Lake and Khibiny

The sheet’s two analyses agree on zirconium and differ seventeen-fold on rare earths. Kipawa Lake, Canada, prints ZrO2 11.80% and Khibiny massif, Russia, 11.83%: worked with Zr 91.224 and O 15.999, that is 8.74% and 8.76% zirconium by mass. Rare-earth oxides, printed as RE2O3, are 6.40% at Kipawa Lake against 0.37% at Khibiny, and FeO runs the other way, 2.41% against 5.32%. Both analyses carry chlorine, 1.47% and 1.82%, and the name, from the Greek for easily dissolved, records its ready dissolution in acids.

What the analyses do not print. Neither lists uranium or thorium. Whether eudialyte is radioactive is answered from a measured study on is eudialyte radioactive, which quotes the regulators rather than advising; general guidance is on is my mineral radioactive. This is not health, safety or legal advice.

Where to go next. Other zirconium silicates on this site include zircon; the full list is in the species index. We hold no catalogue and nothing here is offered for sale; the wanted list is the only commercial route.

Questions