University of Oulu

Huhta, A., Tuisku, P., Balic-Zunic, T., Kärki, A. (2019) Magnesite soapstone in use of fire chamber constructions: composition and structure adaptation. Bulletin of the geological society of Finland, 91(1), 101-118. doi:10.17741/bgsf/91.1.004

Magnesite soapstone in use of fire chamber constructions : composition and structure adaptation

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Author: Huhta, Anne1; Tuisku, Pekka1; Balic-Zunic, Tonci2;
Organizations: 1Oulu Mining School, University of Oulu, P.O. Box 3000, 90014 University of Oulu, Finland
2Department of Geosciences and Natural Resource Management, University of Copenhagen, Øster Voldgade 10, DK-1350 Copenhagen K
3Kivitieto Oy, Teknologiantie 1, 90590 Oulu, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 2.1 MB)
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Language: English
Published: The Geological Society of Finland, 2019
Publish Date: 2019-10-29


The Finnish soapstone industry has found through practical experience that the surface of the magnesite soapstone used in fire chambers and funnels hardens over time. We have studied a magnesite soapstone used in a fireplace continuously for 60 years. The mineralogical changes, that took place during heating and subsequent cooling of the fireplace have been investigated with electron probe microanalyzer and X-ray diffractometer to find an explanation, what kind of reactions caused the hardening. We found that ferromagnesite has been altered to pseudomorphic aggregates composed of ferropericlase and magnesioferrite in the nearest ~30 mm from the surface exposed to fire. Iron has been mobilized in the uppermost 3 mm, enriched in the rims, and depleted from the cores of the ferropericlase aggregates. Magnesioferrite occurs preferably in the fire chamber side of the aggregates in the uppermost 0.20 mm. Talc rims are altered to forsterite and/or enstatite in the reaction with ferromagnesite or its alteration products in the uppermost ~1 mm. In addition, wood combustion gases caused considerable enrichment of zinc and potassium in the chamber surface rock to the depth on 0.20 mm and 3 mm, respectively. The enrichment occurred by crystallization of Zn bearing ferropericlase and magnesioferrite and by crystallization of K bearing sheet silicates.

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Series: Bulletin of the Geological Society of Finland
ISSN: 0367-5211
ISSN-E: 1799-4632
ISSN-L: 0367-5211
Volume: 91
Pages: 101 - 118
DOI: 10.17741/bgsf/91.1.004
Type of Publication: A1 Journal article – refereed
Field of Science: 1171 Geosciences
Funding: This research was supported by K.H. Renlund Foundation, Fund for Quality Improvement of Building Products and Juhani Lehikoinen Foundation, which all are gratefully acknowledged. We thank also Pentti Hölttä and Heikki Pirinen for their useful and constructive comments.
Copyright information: © 2019 The Authors. All published content of BGSF is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.