Edenite or edenitic hornblende is a double chain silicate mineral of the amphibole group with the general chemical composition NaCa2Mg5(Si7Al)O22(OH)2. Edenite is named for the locality of Edenville, Orange County, New York, where it was first described.[4]
| Edenite | |
|---|---|
 Edenite crystal from Bancroft District, Ontario | |
| General | |
| Category | Amphibole mineral |
| Formula (repeating unit) | NaCa2Mg5(Si7Al)O22(OH)2 |
| IMA symbol | Ed[1] |
| Strunz classification | 9.DE.15 |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (same H-M symbol) |
| Space group | C2/m |
| Unit cell | a = 9.83, b = 17.95 c = 5.3 [Å], β = 105.18°; Z = 2 |
| Identification | |
| Formula mass | 834.25 g/mol |
| Color | White to gray, pale to dark green, also brown and pale pinkish-brown |
| Crystal habit | Prismatic crystals, fibrous, as reaction rims on pyroxenes |
| Twinning | Simple or multiple parallel to {010} |
| Cleavage | Good on (110) |
| Fracture | Conchoidal |
| Tenacity | Brittle |
| Mohs scale hardness | 5–6 |
| Luster | Vitreous |
| Streak | White |
| Diaphaneity | Semitransparent |
| Specific gravity | 3.05–3.37 |
| Optical properties | Biaxial (+) |
| Refractive index | nα = 1.606 – 1.649, nβ = 1.617 – 1.660, nγ = 1.631 – 1.672 |
| Birefringence | δ = 0.025 |
| Pleochroism | Distinct, greens, blue-greens, and yellow-browns |
| 2V angle | 50–82° |
| References | [2][3][4][5] |
Occurrence
editEdenite has been found primarily in metamorphic rocks, occurring in pods of other magnesium-rich minerals within a marble formation or with garnet-rich lherzolites from deep within the Earth's crust.[6][7] Thus, finding edenite in the field can indicate high-temperature regional metamorphism of the surrounding rocks.
Uses and importance
editWhile edenite is not important for commercial or industrial applications, it is often studied because of its unique chemical substitution properties. Results from research performed on amphiboles have shown that edenite is particularly suited for fitting chloride anions into its chemical framework.[8] This makes edenite a good candidate for use in chlorine isotope fractionation in amphibole-bearing rocks. Many synthetic variations of edenite are also used in geochemical research to produce a boron analogue of fluoroedenite.[9]
Crystal habit
editEdenite is a member of the monoclinic crystal system and is in the crystal class 2/m (space group C2/m).[6] This means crystalline edenite is symmetrical around a two-fold rotation axis that is then reflected across a mirror plane perpendicular to the long axis of the mineral.[10]
Optical properties
editEdenite is a biaxial positive mineral. When viewed in thin section with a petrographic microscope, it is white-gray with pale green pleochroism in plane-polarized light. Under crossed polars, its interference colors range from first order gray to first order blue.[3]
References
edit- ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
- ^ Edenite Handbook of Mineralogy
- ^ a b Edenite on Mindat.org
- ^ a b Edenite on Webmineral
- ^ IMA Master List
- ^ a b Oberti, R.; Cámara, F.; Della Ventura, G.; Iezzi, G. & Benimoff, A.I. (2006). "Parvo-mangano-edenite, parvo-manganotremolite, and the solid solution between Ca and Mn2+ at the M4 site in amphiboles" (PDF). American Mineralogist. 91 (4): 526–532. Bibcode:2006AmMin..91..526O. doi:10.2138/am.2006.1905. S2CID 55824304.
- ^ Yang, J. (2003). "Relict edenite in a garnet lherzolite from the Chinese Su-Lu UHP metamorphic terrane: Implications for metamorphic history" (PDF). American Mineralogist. 88 (1): 180–188. Bibcode:2003AmMin..88..180Y. doi:10.2138/am-2003-0121. S2CID 133200002. Archived from the original (PDF) on 2012-03-29.
- ^ Oberti, R.; Hawthorne, F.C.; Cannillo, E. & Cámara, F. (2007). "Long-Range Order in Amphiboles". Reviews in Mineralogy and Geochemistry. 67 (1): 125–171. Bibcode:2007RvMG...67..125O. doi:10.2138/rmg.2007.67.4.
- ^ Oberti, R.; Della Ventura, G. & Cámara, F. (2007). "New Amphibole Compositions: Natural and Synthetic". Reviews in Mineralogy and Geochemistry. 67 (1): 89–124. Bibcode:2007RvMG...67...89O. doi:10.2138/rmg.2007.67.3.
- ^ Klein, C., and Dutrow, B. (2007) The 23rd Edition of the Manual of Mineral Science, John Wiley and Sons, Inc. Hoboken, New Jersey, U.S.