Tuesday, October 14, 2008

The Basics of Soapstone

Every Tulikivi fireplace is composed of soapstone. The question is, why soapstone, what is it?

Over 2.8 billion years ago there was a sea where Tulikivi Headquarters stands today. The earth's crust broke up repeatedly and erupted magnesium-rich lava at 1600°C which spread out across the seabed. In the depths of the streams of lava the liquid rock crystallized into coarse-grained olivine - the first step towards the formation of soapstone. Hundreds of millions of years passed. Then, two billion years ago, two continental plates collided, resulting in a mountain range very similar to the Alps.

The seams of lava were "folded" into the earth to a depth of 10,000 m, where pressure as high as 4000 atmospheres and temperatures as high as 500°C. Water solutions containing carbon dioxide seeped deep down through the pores of the rock, and over the course of many millions of years transformed the olivine firstly into serpentine and then into unique Finnish soapstone. Nature created a product as good as one could imagine: a firestone which absorbs the heat of fire particularly quickly, retains it for a phenomenal length of time, and radiates it gradually as gentle radiant heat.

The science? Soapstone has a specific weight of 2980 kg/m3 and thermal conductivity of 6.4 W/mK. This means that soapstone acts like a thermal battery - burn a fire in the firebox until the stove is "charged," (usually 2-3 hours) let the fire go completely out, shut down the damper, and let the charged soapstone radiate out the gentle and warming heat.

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