| Gehlenite | |
|---|---|
| General | |
| Category | Sorosilicates, Calcium minerals, Aluminium minerals |
| Chemical formula | Ca2Al[AlSiO7] |
| Identification | |
| Color | yellow-brown, green-grey, colourless |
| Crystal system | Tetragonal |
| Cleavage | Distinct/good |
| Mohs scale hardness | 5-6 |
| Luster | vitreous, greasy |
| Streak | white, grey-white |
| Birefringence | δ = 0.010 |
Gehlenite, (Ca2Al[AlSiO7]), is a sorosilicate, Al-rich endmember of the melilite complete solid solution series with akermanite.[1][2] The type locality is in the Monzoni Mountains, Fassa Valley in Trento Province in Italy,[2] and is named after Adolf Ferdinand Gehlen by A.J. Fuchs in 1815.[3]
Geological Occurrence[]
Gehlenite is found in carbonaceous chondrites from which it condensed as a refractory mineral in the hotter stages (FU Ori) of the presolar nebula [4], and is found in diorite intruded carbonate rocks [5], and to a far lesser extent in uncompahgrites [6], melilitites [6], alnoites [7], lamprophyres and possibly kimberlite pipes.[8]
Gehlenite has also been found on the comet 81P/Wild.[9]
Crystallography, Composition and Physical Properties[]
Gehlenite is one of five, isostructural tetragonal crystal system minerals in the melilite group. The tetrahedral linkage within the structure is similar to that of an aluminosilicate framework structure[10] and was once considered a feldspathoid-like mineral[11] due to silica undersaturation.
Gehlenite has a Mohs hardness of 5-6, a vitreous to greasy lustre, distinct to good cleavage and is yellow brown, greenish grey or colourless. Its streak is white or grey-white. [2] It is uniaxial (-), has an anomalous nonzero 2V angle and has a characteristic 'ultrablue' birefringence.[10]
References[]
- ↑ Deer et al, 1993
- ↑ 2,0 2,1 2,2 Gehlenite: Gehlenite mineral information and data
- ↑ Dana et al 1997
- ↑ Grossman L (1972) Condensation in the primitive solar nebula, Geochemica et Cosmochemica Acta, 36, 597-619
- ↑ Carmichael ISE, Turner FJ, Verhoogen J (1974) Igneous Petrology, 37
- ↑ 6,0 6,1 Le Maitre RW (2002), Igneous Rocks, 11, 153
- ↑ Nixon PH (1987) Mantle Xenoliths, 102-103, 336, 450-451
- ↑ Skinner EMW, Mahotkin IL, Grutter HS (1999) Melilite in Kimberlites, Proceedings of the International Kimberlite Conference, 7, 788-794
- ↑ Mindat page for Comet Wild 2 (Comet 81P)
- ↑ 10,0 10,1 Louisnathan S (1969), Refinement of the crystal structure of gehlenite, Canadian Mineralogist, 10, 822-837
- ↑ Best MG (2003), Igneous and Metamorphic Petrology (2nd Ed), 398, 693, 702-703
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it:Gehlenite nl:Gehleniet uk:Ґеленіт