Structural and chemical contrasts between prismatic and fibrous fluoro-edenite from Biancavilla, Sicily, Italy
Structural and chemical contrasts between prismatic and fibrous fluoro-edenite from Biancavilla, Sicily, Italy
The Canadian Mineralogist (April 2007) 45, Part 2: 249-262
- amphibole group
- cell dimensions
- chain silicates
- clinoamphibole
- crystal chemistry
- crystal form
- crystal structure
- edenite
- Europe
- formula
- Italy
- lattice parameters
- Mossbauer spectra
- Mount Etna
- richterite
- Rietveld refinement
- SEM data
- Sicily Italy
- silicates
- Southern Europe
- spectra
- X-ray diffraction data
- fluoro-edenite
Fluoro-edenite, NaCa (sub 2) Mg (sub 5) (Si (sub 7) Al)O (sub 22) F (sub 2) , occurs with both prismatic [A.M.86-1489] and fibrous morphologies in altered volcanic products at Monte Calvario, on the flanks of Mt Etna, Sicily. New crystal-chemical and structural data are reported for the fibrous variety. SEM-EDS microanalyses and Moessbauer spectroscopy indicate a variable composition for the fibres, ranging mostly from fluoro-edenite to winchite, tremolite and richterite compositions. From a combination of the microchemical, Moessbauer Fe (super 3+) /Fe (sub tot) values and crystal structure refinement, the chemical formula is (Na (sub 0.307) K (sub 0.157) )(Ca (sub 1.505) Na (sub 0.495) )( (super [6]) Al (sub 0.104) Fe (super 3+) (sub 0.333) Fe (super 2+) (sub 0.162) Mg (sub 4.255) Ti (sub 0.062) Mn (sub 0.063) )(Si (sub 7.520) (super [4]) Al (sub 0.480) )O (sub 22) (F (sub 1.970) Cl (sub 0.020) ). The cell parameters and site scattering were refined. Fe (super 2+) was assigned to the M2 and M3 sites, and all Fe (super 3+) was assigned to the M2 site. The Fe (super 2+) content of each M2 site is far greater than that of M3. The interactions between mineral fibre and the biological environment are related strongly to the crystal chemistry of this fibrous amphibole.
