tuhkakivi

Tuhkakivi is a Finnish term that translates to "ash stone" or "volcanic ash rock". It refers to a type of rock formed from consolidated volcanic ash. When volcanic eruptions occur, they expel large quantities of ash, which is composed of fine fragments of rock, minerals, and volcanic glass. This ash can travel great distances and settle on the landscape. Over time, with pressure and possibly cementation by minerals dissolved in groundwater, these ash layers can lithify, transforming into a solid rock.

Tuhkakivi is a type of tuff, which is a general term for volcanic ash that has become a rock. The specific properties of tuhkakivi can vary depending on the composition of the ash, the size of the particles, and the degree of consolidation. It can range in color from light gray to dark brown or black, and its texture can be fine-grained and porous or coarser and more consolidated. Due to its volcanic origin, tuhkakivi is often found in regions that have experienced past volcanic activity. It has been used historically in some areas for building materials, though its relatively soft and porous nature can limit its durability compared to other stones.