Diversity of soapstones: Classification and thermal behavior

Thesis event information

Date and time of the thesis defence

Place of the thesis defence

Linnanmaa, hall IT115

Topic of the dissertation

Diversity of soapstones: Classification and thermal behavior

Doctoral candidate

Master of Science Anne Huhta

Faculty and unit

University of Oulu Graduate School, Faculty of Technology, Oulu Mining School

Subject of study

Geology and mineralogy


Professor Olav Eklund, Åbo Akademi University


Research professor Seppo Gehör, University of Oulu

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Diversity of Soapstones: Classification and Thermal Behavior

Currently, the term ”soapstone” often refers to talc rich rocks, having still a wide range of variation in mineral composition. As a result, the name provides little information on the major mineral constituents in the rock. Therefore, unambiguous classification and nomenclature scheme was developed. In addition to scientific discussion, the new method fulfills the need of the soapstone industry by allowing them to name the material they are using. Capacity to withstand high temperatures varies greatly between different soapstone types.

In addition to talc, thermal durability is affected by other minerals and structures occurring in soapstones. A new test method was developed to study thermal shock resistance of fine-grained magnesite soapstones. The most significant attributes were microscopic folding and mesh-like texture of talc by increasing the thermal shock resistance of the rock.

A magnesite soapstone used as a construction material in fire chamber walls for over 60 years was studied. With decades of experience, soapstone industry has learned that the surface layer of magnesite soapstone hardens over time in the fire chamber conditions. Increased hardness and durability are due to reactions between minerals occurring in the rock and formation of new minerals. For example, later formed mineral grains filled the microscopical pores of the surface layer of the rock. In addition, certain components of firewood have participated in hardening process of magnesite soapstone surface layer via combustion gases.

Black carbon particles accelerate the climate change. For reduction of emissions, special attention should be paid to quality and condition of fireplaces and fire chambers used as residential warming. Magnesite soapstone formed by geological processes allows the use of fireplaces in extremely high temperatures. Furthermore, taking care of efficient burning with appropriate direction of air, it is possible to achieve close to particulate-free combustion.
Last updated: 1.3.2023