Tufa

Tufa - (from Italian. Tufo) is a light, coherent, porous rock. Having high decorative properties, tufa is important finishing construction material. Using method of geological formation, tufa can be classified: volcanic, calcareous and cherty. Calcareous and cherty tufas, as against volcanic tufas, combine group of rock formation. This group is got together by genesis, in other words it`s the accretion of calcium carbonate or substance of cherty from solution in the places of egressing of mineral wells on the earth.


Condition of formation

As a result of wearing-away of rock formation water dissolves chemical compounds, forming a solution, which transforms a secondary precipitation and after this process new rocks create.


If aggradations are the result of inorganic chemical processes, tufa and« scale» occur. In the places of discharge of water sources the pressure decreases, carbon dioxide is removed from the solution. As consequence dissolved in water combinations decompose and precipitate in the form of calcareous or cherty tufas.

Dripstones and stalagmites are formed from Tufas of the caves. Balls of calcareous spar can gather in masses and form so-called pea stones, which are classified to oolite.


Varieties of Tufa


  • Calcareous tufa (travertine) — formed in accretions in case of high calcium carbonate saturation in the surface water. Calcareous tufa often originates in the place of natural barriers, where freshwater crops up, in consequence of which characterized by spotty sediment s and «cascades». Plants, which grow near spring-well can be covered by it. The most famous mine fields of this solid with «cascades» are Hierapolis (Turkey) and Armenia. Calcareous tufa can be yellow-brown and cream-coloured.
  • Quartz sinter (geyserites). Silicon compounds, falling out of the geysers as a result of cooling and evaporation form quartz sinter. Earth silicon of the spring-well forms amorphous opal or sometimes calcedony.

Application

Having low sound conductivity and thermal conductivity, bondless, pored calcareous tufas are used as constructional materials; travertine is used in the production of floor and faced tiles. For erection of construction building stone is made from calcareous tufa, for production of calcium lime thermal insulating material is too made from calcareous tufa. From the earliest times blocks of tufa used for building. Tufa is the one of free-cutting stones; it is used for construction of Monolithic Church of Lalibela. Then again tufas are partially permeable, this fact place limits on using of tufas as ornamental stone.