Oriented transformation of grunerite to clinoferrosilite at 775° C and 500 bars Argon pressure
✍ Scribed by Subrata Ghose; Jerry R. Weidner
- Publisher
- Springer
- Year
- 1971
- Tongue
- English
- Weight
- 886 KB
- Volume
- 30
- Category
- Article
- ISSN
- 0010-7999
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✦ Synopsis
A member of the grunerite series (F%.68~lVfno.142Ca0.n0Mg0.096) (SiT.96sA10.016)O22(OH)2, has been transformed to clinoferrosilite, amorphous silica and water at 775 ~ C and 500 bars Argon pressure. Single crystal photographs of an oriented intergrowth of the amphibole and pyroxene show that the clinoferrosilite retains the crystallographic a, b and c axes of the original grunerite in the I2/m orientation and has the cell dimensions: a=9.77, b-9.08, c ~ 5.30 ,~, fl = 109.5~ space group P21/c. MSssbauer resonance spectroscopy confirmed the identity of the clinoferrosilite.
A transformation mechanism requires a minimum of ionic movements in an acceptor region (7/8 of the total crystal), where pyroxene is formed by expulsion of protons and acceptance of Fe 2+ ions; simultaneous destruction of donor regions provide the Fe e+ ions, the residue being silica and water. The formation of metastable clinoferrosilite rather than fayalite and quartz indicates the strong structural control imposed by the host grunerite structure on the nature of the transformation products.