The Olivine stone
According the tests conducted (under Professor Heikki Niini) in the laboratory for economic geology at the University of Technology, the olivine is homogeneous and strong. It is mainly composed of a rare, unusually fresh, hard olivine with excellent capacity to withstand heat. In the rock classification of the geotechnical laboratory of the Technical Research Centre of Finland (VTT/GEO bulletin 25, 1976) the weathering degree of the mäntyharju olivine is 0 (unweathered). The olivine deposit contains abundant microscopically thin chlorite-serpentine veins. These make it easier for the rock to be crushed into sizes appropriate for use in sauna stoves. Thanks to its unusually high density, combined with its good specific heat capacity and heat conductivity, the stone absorbs and dissipates heat at a constant rate and over a long period. Regular heat expansion slows down the mechanical weathering that affects all rocks in the changing temperate of the sauna. The olivine presents no health hazards, not only because it contains no sulphur or minerals but because its uranium content is minimal. This means that carcinogenic gases are not released as they are from other rocks, granites and gneisses in particulary.
General Information of Mäntyharju’s Oliviinioccurrence
The Geological Survey has completed a very thorough investigation of Mäntyharju’s oliviinioccurrence (leaflet No M19/3132/-81/80). Stone states that a chemical- and mineral composition are quite exceptional. Nothing like this haven’t been found in other parts of Finland.
Research has tested a stone sauna units, and finds it very suitable material for the stone oven.
The difference between olivine and olivine diabase
As there are only two types of sauna stones available, we should clarify the difference between them a little.
* The information about the composition of olivine diabase is based on an average of the proportionate shares announced by manufacturers.