The Prospectivity of Building Stone in New England

Building stone is a broad term encompassing many forms of stone used in some type of construction. The history of its use goes back to the Egyptian monuments followed later by the ancient Greek and Romans and subsequent civilizations (e.g. Incas). Although enormous quantities of roughly hewn stone are still used globally for many purposes its use tends to be strictly local. In contrast, there is a huge international trade in another form of stone – dimension stone. This is the form of stone that is produced to a set dimension and finished in numerous ways for that aesthetically driven appearance. Dimension stone touches more people in everyday life than the majority of high profile commodities. Millions of people have daily physical contact with it - walking on it (floors), driving over it (paving), leaning on it (banks and kitchen tops), playing on it (billiard/pool tables), eating off it (hot rock plates) and providing memories of the departed (gravestones).

Any stone that is separated from its last natural source and capable of being and intending to be dimensioned can be a dimension stone. However, to be a commercial dimension stone there is an implication of physical and chemical durability if it is be used in construction because constructions have design lives. In addition to durability the stone must be available in sufficiently large amounts and have a consistency in texture, structure and appearance (colour).

These fundamental characteristics together with the required strengths, capacity for water absorption, and a stable mineralogy generally dictate the type of application for that stone, and in turn this determines whether it is commercially viable. In the past the proximity of a dimension stone to a population centre was important but modern processing and transport techniques allow stone to be sourced from all countries of the world. Ironically, a local quarry at the edge of town may now not be a viable proposition for sourcing stone for construction.

Because stone is a construction material there is a heavy emphasis on the quality of its natural characteristics. Engineers require a plethora of information before committing to construction especially because of its potential small-scale variability. Numerous methods of testing are available and numerous standards have been developed in a number of countries to measure and control these natural characteristics. The stone is subjected to petrographic analysis, compression, flexion, rupture, absorption, expansion, to name a few and may undergo more rigorous scrutiny in laboratories to test for deleterious minerals by X-ray diffraction, freeze-thaw resistance, abrasion resistance, chemical composition, radio-activity and radon evolution, and pulse velocity measurements. Depending on the type of surface finish and its eventual intended application it is also subjected to slip tests and stain tests. It may also be coated with a range of synthetic products.

In addition to the intense laboratory scrutiny field inspections of a stone resource are equally as important when determining commercial viability and product acceptability. It must be possible to extract the stone from its resource, consistently, to a fairly set size, profitably, and without damage to the product. Natural features and flaws must be avoided and subtle variations must be recognized. Natural or induced fractures are particularly detrimental to an operation because of the down-the-line financial ramifications.

Naturally different stones have different characteristics and requirements, have different applications and require different expertise and machinery for extraction. On top of this there are the fickleties of sales, weather, machinery performance, landholder demands, environmental restrictions, government rules and regulations. It’s a wonder that anyone bothers at all in getting a stone resource off the ground.