The confusion … between hardness and toughness has led to serious practical errors in the choice of materials for roads, inasmuch as the attention has been often directed exclusively to their hardness, without any regard being had of their toughness.
Charles Penfold, 1840, A Practical Treatise on Best Mode of Repairing Roads, p.11.
{{image2-a:r-w:220}}Following its successful use in the Vermont State House, Barre granite had attracted interest by the late 1830s. Another boost to the fledgling industry came in 1839 with a contract for 10 million paving blocks for the City of Troy, New York.
As early as 1663, Boston had roads paved with round cobblestones used as ballast in European ships. But experience at the time demonstrated that the most enduring streets for heavy traffic in cities were not paved with cobblestones, but rectangular stone blocks 76mm to 101mm wide, 152mm to 178mm thick and 203mm to 305mm long. Streets paved with cobblestones were difficult to repair, hard on horses and rougher on wagons than rectangular block pavements.
Specifications for paving stones required rectangular faces and nearly straight edges. The corresponding dimensions of opposite faces could not vary more than 13mm, and the surface had to be free from bunches or depressions exceeding 13mm.
Paving blocks had to be hard (being able to resist the friction or grinding of steel-rimmed wheels moving along them), as well as tough (being able to withstand the pounding or crushing action of horse hooves).
{{image3-a:r-w:220}}But even if a rock was hard and tough, some rocks became smooth and glazed under traffic, affording a poor foothold for horses. The best paver blocks were not only hard and tough but wore roughly, thus affording horses good traction.
The feldspars in Barre granite tended to fracture and create tiny depressions, while the stronger quartz crystals stood proud. This gave Barre granite the right degree of “tooth” for use as paving blocks.
Even though paving breakers did not need to possess the stonemason’s fine workmanship, they were highly skilled workers. Quickness in seeing and taking advantage of the natural splitting characteristics of the rock, as well as deftness in handling the necessary tools, was requisite. A skilled paving breaker could turn out 100 blocks per day.
Paving breakers were usually paid a sum for each 1000 blocks they made. The price paid varied according to the size of block, kind of stone used, if tools were furnished, and whether or not their employers quarried the blocks. In Barre, blocks were almost always provided by the employer from a seemingly endless source of rock:
Standing near the top of Millstone Hill … one may see great mounds of broken granite running up to more than 100 feet in height and covering perhaps an acre or more each, in many directions … On closer inspection each mound is found to be made up of irregular-shaped pieces of [waste] granite that vary from one to several feet in each dimension. Most of this now worthless stock may sometime be readily worked into paving blocks.
Alton D. Adams, 1906, Wealth in Barre Granite, Mines and Minerals, p. 487.