ACTINOLITE

Ca₂ (Mg,Fe)₅ Si₈ O₂₂ (OH)₂

The idealised actinolite chemical formula, Ca₂(Mg,Fe)₅Si₈O₂₂(OH)_2, is rarely encountered in natural samples. There are generally appreciable amounts of Al³⁺, Fe³⁺, Mn, Cr and Na in these minerals.¹ The actinolite crystal structure is monoclinic with space group C2/m and consists of two unique tetrahedral sites (T1,T2), four unique octahedrally coordinated sites (M1,M2, M3 and M4), and one 12-coordinated site (A) ². Actinolite has derived its name from the Greek word for ray. 

Actinolite is usually associated with occupational diseases of the lung. Therefore many different analytical techniques, including spectroscopic techniques, have been used in order to allow greater variety of ways to detect it. Analysing major bands in the IR spectrum of actinolite, hydroxyl group bands are observed at 3675, 3660, 3643 and 3625 cm^{-1 3} and M-OH vibrational band is found at 655 cm^{-1 1}. Other vibrational bands include medium to strong absorption at 1103 and 1053 cm^-1, broad doublet at 994 and 956 cm^-1 and medium absorption at 505cm^-1. Minor bands are observed at 920, 756, 682, 465 and 355 cm^{-1 4} . The near-infrared spectrum shows overtones of hydroxyl group at 6945, 7155 and 7185 cm^{-1 5}.

In the Raman spectrum, the strong band at 670-680 cm^-1 is characteristic of the silicon-bridging oxygen-silicon symmetric stretching mode of the pyroxene-type chain. Non-bridging oxygen stretching modes of this silicate network are assigned in the region 900-1100 cm^{-1 6}.             

1.    Mustard, J.F. (1992) Chemical analysis of actinolite from reflectance spectra. American Mineralogist, 77 (3-4), 345-358.

2.    Ghose, S. (1961) The crystal structure of cummingtonite. Acta Crystallographica 14(Part 6): 622-627.  

3.    Farmer,V.C. (1974) Infrared spectra of minerals in Mineralogical Society Monograph 4 VC Farmer (Ed) pp 322. Mineralogical Society, London.

4.    Taylor, D.G., Nenadic, C.M. and Crable, J.V. (1970) Infrared spectra for mineral identification. Amer. Ind. Hyg. Ass., J., 31(1), 100-8. 

5.    Clark, R.N. and King, T.V.V., The use of spectroscopy in environmental geochemical studies. In Doe, and Bruce, Eds. Proceedings of a U.S. Geological Survey workshop on Environmental geochemistry., 79-82. U.S. Geological Survey, Reston, VA. United States.

6.    Blaha, J.J. and Rosasco, G.J. (1978) Raman microprobe spectra of individual microcrystals and fibers of talc, tremolite and related silicate minerals. Anal. Chem., 50 (7), 892-6.

SELECTED REFERENCES ON SPECTROSCOPY OF ACTINOLITE:  

2.    Taylor, D.G., Nenadic, C.M. and Crable, J.V. (1970) Infrared spectra for mineral identification. Amer. Ind. Hyg. Ass., J., 31(1), 100-8. 

3.    Clark, R.N. and King, T.V.V., The use of spectroscopy in environmental geochemical studies. In Doe, and Bruce, Eds. Proceedings of a U.S. Geological Survey workshop on Environmental geochemistry., 79-82. U.S. Geological Survey, Reston, VA. United States.

4.    Wang, A., Dhamelincourt, P. and Turrell, G. (1988) Raman microspectroscopic study of the cation distribution in amphiboles. Appl. Spectrosc., 42(8), 1441-50.

Original spectra shown for this mineral can be obtained on request from J.T. Kloprogge (E-mail t.kloprogge@qut.edu.au), or R.L. Frost (E-mail r.frost@qut.edu.au).

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