1. Clino-Amphiboles (Monoclinic Amphiboles) A 0-1 B 2 C 5 T 8 O 22 (OH,F,Cl) 2 Presented by Joyleen Desai Paul Sandlin

2. Structure Space group: C2/m T1: dk blue T2: lt blue M1: orange M2: dk green M3: yellow M4: lt green A: purple O1, O2, O4: red (non-bridging) O5, O6, O7: pink (bridging) O3: OH, Fl, Cl, O 2-

3. Crystallographic Sites AM4M3M1M2T1T2O4 Coordination 126-866644 Cation Preference KNaMn Al SiOH NaCaFe 2+ TiSiAlF MnMg Fe 3+ Cl Fe 2+ Mg Fe 2+ Source: Spear (1995)

4. Structural Cell Parameters MineralFormulaa ang b ang c ang βρ g/cm 3 (calc) V ang 3 Z Hornblende (Na,K) 0-1 (Ca,Na,Fe, Mg) 2 (Mg,Fe,Al) 5 (Si,Al) 8 O 22 (OH) 2 9.88718.1745.308105 2.96921.28 2 Cummingtonite (Mg,Fe) 7 Si 8 O 22 (OH) 2 9.53418.2315.323102 3.13905.182 Grunerite Fe 7 Si 8 O 22 (OH) 2 9.5718.225.33102 3.66908.722 Tremolite Ca 2 Mg 5 Si 8 O 22 (OH) 2 9.8318.055.27105 2.98906.642 Actinolite Ca 2 (Mg,Fe) 5 Si 8 O 22 (OH) 2 9.8418.15.28105 3.2909.612 Glaucophane Na 2 Mg 3 Al 2 Si 8 O 22 (OH) 2 9.54117.745.3104 2.99870.832 Riebeckite Na 2 (Fe,Mg) 3 (Fe,Al) 2 Si 8 O 22 (OH) 2 9.7718.035.34104 3.4914.242 Source: www.webmineral.com

5. Amphibole Occurrences Source: Spear (1995)

6. Hornblende (Na,K) 0-1 (Ca,Na,Fe,Mg) 2 (Mg,Fe,Al) 5 (Si,Al) 8 O 22 (OH) 2 Common in igneous rocks –Essential in intermediate composition igneous rocks Metamorphosed mafic rocks –Amphibolite facies associated with plagioclase Hornblende is the name given to amphiboles with an indeterminate composition

7. Cummingtonite Series Cummingtonite: (Mg,Fe) 7 Si 8 O 22 (OH) 2 Grunerite: Fe 7 Si 8 O 22 (OH) 2 Occur in med-grade metamorphism –Grunerite found in metamorphosed Fe- rich sediments Grunerite is less pleochroic M4 (yellow) takes Mg in cummingtonite structure

8. Actinolite Series Tremolite: Ca 2 Mg 5 Si 8 O 22 (OH) 2 Actinolite: Ca 2 (Mg,Fe) 5 Si 8 O 22 (OH) 2 Found in med-grade metamorphosed mafic rocks –Calcic amphiboles are the most abundant in greenschist and amphibolite facies Tremolite is one of the first minerals to form in metamorphosed carbonates –At high T, yields to diopside Fe goes into either M3 or M1 (yellow) in actinolite structure

9. Na-Amphiboles Glaucophane: Na 2 Mg 3 Al 2 Si 8 O 22 (OH) 2 Riebeckite: Na 2 (Fe,Mg) 3 (Fe,Al) 2 Si 8 O 22 (OH) 2 Glaucophane found only in metamorphic rocks –Blueschist facies Riebeckite most common in igneous rocks –Granites and pegmatites Na goes in M4 site –In Riebeckite, Fe and Al in M2 site, Fe and Mg in M3 and M1 sites

10. Expansion and Compression Clino-amphiboles are chemically similar to clino-pyroxenes Thermal expansion is taken up in the M-O bonds parallel to the c-axis

11. Oxidation-Dehydroxylation Dehydrogenation occurs rapidly at high temperatures in amphiboles containing Fe 2+ Proceeds by the reaction Fe 2+ + OH = Fe 3+ + O 2- + ½H 2 Mossbauer spectra suggest that considerable cation disorder accompanies oxidation