Eudialyte
Eudialyte, whose name derives from the Greek phrase Εὖ διάλυτος, eu dialytos, meaning "well decomposable", is a somewhat rare, nine-member-ring cyclosilicate mineral, which forms in alkaline igneous rocks, such as nepheline syenites. Its name alludes to its ready solubility in acid.
| Eudialyte | |
|---|---|
| General | |
| Category | Cyclosilicate |
| Formula (repeating unit) | Na15Ca6(Fe,Mn)3Zr3SiO(O,OH,H2O)3 (Si3O9)2(Si9O27)2(OH,Cl)2 |
| IMA symbol | Eud |
| Strunz classification | 9.CO.10 |
| Crystal system | Trigonal |
| Crystal class | Hexagonal scalenohedral (3m) H-M symbol: (3 2/m) |
| Space group | R3m |
| Unit cell | a = 14.31, c = 30.15 [Å]; Z = 12 |
| Identification | |
| Color | Red, magenta, brown; also blue and yellow |
| Crystal habit | Crystals short rhombohedral to long prismatic, granular, irregular masses |
| Cleavage | Distinct on {0001} imperfect on {1120} |
| Fracture | Uneven |
| Tenacity | Brittle |
| Mohs scale hardness | 5–6 |
| Luster | Vitreous |
| Streak | White |
| Diaphaneity | Transparent to translucent |
| Specific gravity | 2.74–3.10 |
| Optical properties | Uniaxial (+/−) |
| Refractive index | nω = 1.606–1.610 nε = 1.610–1.613 |
| Birefringence | δ = 0.004 |
| Pleochroism | Weak: O= colorless, pale yellow, pink; E= pink to colorless |
| Solubility | H2SO4 |
| Other characteristics | Mildly Radioactive |
| References | |
Eudialyte was first described in 1819 for an occurrence in nepheline syenite of the Ilimaussaq intrusive complex of southwest Greenland.
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