A building block that is as strong as concrete, but a fraction of the weight, readily available in most places, and is fireproof. Too good to be true? No, its called calcareous tufa and the Romans used it as the principal building block in their most important structures. Sadly we have forgotten this stone apart from its brief reappearance in a few churches and cathedrals in the early C13th. The stone is so light they used it to support the roofs in places such as Worcester, and Canterbury cathedrals.
Apart from its construction qualities it is also deemed to have life giving qualities and re-juvenating powers and used extensively by the Crusaders. Interestingly the timing of the Knight Templars expulsion from the Holy Land in the late C12th and early C13th co-incided with the use of calcareous tufa in churches. There are a series of churches using this material extensively in the Teme Valley in Hereford and Worcester.
The photo shows the use of the stone in Moccas church, and also note the exquiste Romanesque tympanum. Shelsley Walsh Church is built substantially from calcareous tufa. Rarely is the stone mentioned in the official historic listings and guides to the churches, and in a conversation with a past Surveyor to the Fabric of Canterbury Cathedral he didn't even know that the material was present.
The material literally forms in front of your eyes, from a water source rich in calcium carbonate which when in contact with the atmosphere and an appropriate catalyst precipates the material forming the rock. The above rock (Southstone Rock at Shelsley Walsh) is an example of this, and is also the way, travertines and various other rock are formed too. This apparent 'growth' or 'stone being given birth to' is the link to its use in grottos in the C18th and C19th landscapes gardens.
Although the rock can be found all over the country and the Romans seemed to be able to find it anywhere they wanted to build their baths, it can be seen in known limestone areas such as Cheddar Gorge, Somerset, Matlock, Derbyshire, Malham Tarn, Yorkshire Dales, and Teme Valley/Golden Triangle, Hereford and Worcester. The photograph is of 'Tufa Cottage' Matlock.