Zussmanite in ferruginous metasediments from southern central Chile

H. J. Massonne, F. Hervé, O. Medenbach, V. Muñoz, A. P. Willner

Research output: Contribution to journalArticlepeer-review

6 Citations (Scopus)

Abstract

Zussmanite KFe13[AlSi17O42](OH)14, a modulated 2:1 layer silicate, has so far been found only in iron-rich metasediments from Laytonville, California (Agrell et al., 1965). A new occurrence is reported here from Punta Nihue north of Valdivia, Chile, in banded stilpnomelane-schists. These are intercalated in the 'Western Series', a complex of low-grade metamorphic rocks with local high-pressure, low-temperature overprint (e.g. blueschists). The rock contains conspicuous porphyroblasts of zussmanite of mm size and is composed of chemically distinct bands with the subsequent assemblages: (1) zussmanite-stilpnomelane-quartz, (2) siderite-quartz±stilpnomelane (3) apatite-stilpnomelane-quartz±siderite. The chemical composition of zussmanite, (K0.80Na0.05Ba0.01)(Fe11.29 2+Mg1.11Mn0.25Fe0.14 3 +Cr0.01Al0.19Ti0.01)[Al1.23Si16.77O42](OH)14, its optical properties and X-ray data correlate well with the Californian occurrence. Additionally, we present new IR data. In type (2) bands of fine-grained crystals of a K,Al poor mineral formed from siderite and quartz. Its chemical composition is close to that of zussmanite. A similar phase was also reported from Laytonville, California (Muir Wood, 1980). The rarity of rock-forming zussmanite can be explained by its occurrence in strongly Fe-rich and reduced rocks, as well as, by a possibly narrow P-T stability field.

Original languageEnglish
Pages (from-to)869-876
Number of pages8
JournalMineralogical Magazine
Volume62
Issue number6
Publication statusPublished - Dec 1998

Keywords

  • Chile
  • Metasediments
  • Punta Nihue
  • Schist
  • Zussmanite

ASJC Scopus subject areas

  • Geochemistry and Petrology

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