Gonnardite
Gonnardite is a comparatively rare, fibrous zeolite, natrolite subgroup. Older papers claim that a complete solid solution exists between tetranatrolite and gonnardite, but tetranatrolite was discredited as a separate species in 1999. A series, based on the disorder of the silicon-aluminum in the framework, appears to exist between Na-rich gonnardite and natrolite, Na2(Si3Al2)O10·2H2O.
| Gonnardite | |
|---|---|
Gonnardite from the Bundoora Quarry, Victoria, Australia. Specimen size 4.9 cm | |
| General | |
| Category | Tectosilicate |
| Formula (repeating unit) | (Na,Ca)2(Si,Al)5O10·3H2O |
| IMA symbol | Gon |
| Strunz classification | 9.GA.05 (10 ed) 8/J.21-40 (8 ed) |
| Dana classification | 77.1.5.7 |
| Crystal system | Tetragonal |
| Crystal class | Scalenohedral (42m) H-M symbol: (4 2m) |
| Space group | I42d |
| Unit cell | a = 13.38 c = 6.66 [Å]; Z = 2 |
| Identification | |
| Color | Colorless, white, yellow or pink to salmon orange |
| Crystal habit | Radiating fibrous; massive |
| Mohs scale hardness | 4 to 5 |
| Luster | Vitreous to silky or dull |
| Streak | White |
| Diaphaneity | Translucent |
| Specific gravity | 2.21 to 2.36 |
| Optical properties | Biaxial (+) |
| Refractive index | nα = 1.514, nβ = 1.515, nγ = 1.520 |
| Birefringence | δ = 0.006 |
| 2V angle | Measured, 52° |
| References | |
Gonnardite was named in 1896 after Ferdinand Pierre Joseph Gonnard (1833–1923), who was Professor of Mining Engineering at the University of Lyon, France.
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