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Potassium-fluor-richterite, a new amphibole from San Vito, Monte Somma, Campania, Italy

Potassium-fluor-nchterite, un nuovo anfibolo da San Vito, Monte Somma, Campania, Italia

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Abstract

Potassium-fluor-richterite occurs as euhedral crystals, light-grey in colour, in a skarn ejectum from a pyroclastic deposit near S. Vito, Monte Somma, Naples. It is associated with diopside and calcite. The strongest X-ray diffraction lines are (d- spacing in Å): 3.166, 8.49, 3.288, 2.831, 1.918 and 1.633. The cell parameters (in Å, space groupC2/m) are:a = 9.978 (1);b = 17.991(2);c = 5.269 (1); ß(°) = 104.90 (2);V = 914.2 (3). Potassium-fluor-richterite is biaxial negative with (± 0.004) nX = 1.613; nY = 1.623; nZ = 1.630. The crystal-chemical formula is:

(K0.67Na0.34) (Ca1.09Na0.91) (Mg40.976Fe0.017Mn0.002) (Si7.94Al0.04Ti0.007) O22 (F1.35OH0.65).

The FTIR spectrum in the OH-stretching region is discussed.

Riassunto

La potassium-fluor-richterite si rinviene in proietti carbonatici metamorfosati e metasomatizzati contenuti in un deposito piroclastico affiorante vicino al Comune di S. Vito, Monte Somma, Napoli. È associata con diopside e calcite. I riflessi più intensi nello spettro misurato ai raggi X sono (distanze interplanari in Å): 3.166, 8.49, 3.288, 2.831, 1.918 e 1.633. I parametri di cella sono (in Å):a = 9.978 (1);b = 17.991 (2);c = 5.269 (1); ß(°)= 104.90 (2);V = 914.2 (3). La potassium-fluor-richterite è biassica negativa. Gli indici di rifrazione sono (± 0.004): nX = 1.613; nY = 1.623; nZ = 1.630. La formula cristallochimica è: (K0.67Na0.34) (Ca1.09Na0.91) (Mg40.976Fe0.017Mn0.002) (Si7.94Al0.04Ti0.007) O22 (F1.35OH0.65). Lo spettro FTIR nella regione di stiramento dell’OH viene discusso. mis|Nella seduta dell’8 febbraio 1992.

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Correspondence to Giancarlo Della Ventura or Gian Carlo Parodi or Adriana Maras or A. Mottana.

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Ventura, G.D., Parodi, G.C., Maras, A. et al. Potassium-fluor-richterite, a new amphibole from San Vito, Monte Somma, Campania, Italy. Rend. Fis. Acc. Lincei 3, 239–245 (1992). https://doi.org/10.1007/BF03001570

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Key words

  • Potassium-fluor-richterite
  • Monte Somma
  • Amphibole
  • Physical properties
  • FTIR