Gibraltar’s Black Granite

Some black and white pictures and an old memo in government files were all the evidence we could find of a mysterious black granite quarry in Gibraltar, Halifax County.

Gerald F. Murphy from the Nova Scotia Technical College visited the quarry on July 12, 1922. He described its location as just north of “a small settlement known as Gibraltar,” about ten miles north of Musquodoboit Harbour. Murphy wrote that the Dartmouth to Musquodoboit Harbour railway line passed within a few hundred yards of the quarry, which suggests the quarry was close to highway 357. Part of that rail line is the Musquodoboit Trailway today.

Murphy inspected the quarry because of its potential to provide stone for monuments and decorative purposes. A number of quarries in Nova Scotia have provided “black granite” for this purpose because it can be polished to a brilliant black luster, ideal for things like headstones, kitchen counters and floor tiles.

Such stone is often sold under the name “black granite,” which describes its appearance but is inaccurate because the stone is not usually granite. Many Nova Scotian quarries that provided stone for monuments actually contained a rock called gabbro, but the Gibraltar quarry’s deposit was quartzite.

In a memo written after his inspection, Murphy referred to the Gibraltar stone as “so-called Black Granite” and points out that the name is incorrect.

At the time of his visit, the quarry’s face was only 25 feet high and had been worked briefly to extract just 100 tons. Murphy’s inspection was intended to help determine whether the quarry could be worked on an ongoing basis.

He wrote that the quarry’s location was excellent. Its proximity to the railway would make transporting stone easy and inexpensive. A nearby stream could provide water for generating steam power. The hill being quarried had an elevation of about 175 feet above the railroad, which suggested there would be a large quantity of stone available: “There were not sufficient exposures to make even an approximate guess at the tonnage, but…it would be safe to say that the supply would be sufficient for many years and no trouble need be feared in this respect.”

However, the quarry had challenges. The rock was fractured, but Murphy believed it was “surface fracturing” – cracks in the stone caused by “surface action” such as weathering and frost heaving. He believed the fracturing “would disappear in ten or twenty feet as stone was extracted.”

Of greater concern were nodules of pyrite (aka fool’s gold) in the deposit because they oxidized when exposed to air and left rusty stains on the rock. Rock for monuments, decorative purposes and stone buildings needs to be solid and attractive, without stains, joints/cracks, veins or other characteristics that are considered undesirable. When we blast and crush rock like gypsum for use in wallboard, or aggregate for use in construction, things like cracks and stains do not matter because we break the rock down anyway and combine it with other materials. But stone used for these other purposes needs to be as flawless as possible.

Murphy wrote, “The pyrite however is serious. How serious it is, can only be determined by further work to demonstrate if sufficient materials free from pyrite can be obtained. Pyrite as it occurs in nodules practically prohibits the use of the stone for monumental or decorative purposes. It would be possible to obtain stone free from pyrite in the face exposed at present but it will have to be determined how much waste rock will be produced in obtaining this pyrite free material.”

Despite the fracturing and pyrite concerns, Murphy still believed the quarry merited additional investment and work: “The rock when polished takes a beautiful black appearance and should prove very attractive for monumental and decorative purpose. I would therefore recommend that the present plant be put in working condition and a face prepared about 100 feet wide and 50 feet in height. This will give a fair exposure of the rock which is lacking at present, and you will be better able to determine how the pyrite will affect the value of your product. This should be determined before going to the heavy expense of permanent equipment.”

The memo included the four pictures below. The landscape picture was taken from the railroad and shows the general area, with the very top of the quarry face visible behind the trees in the middle. The picture of the building shows the boiler house and part of the quarry in the background. The two close ups of the quarry face show the fractures in the rock.

Murphy’s memo is apparently the only historical document about the Gibraltar quarry in Department of Mines records, which indicates that the operation was short-lived, perhaps due to the challenges created by the pyrite and/or financial issues.

We believe the Gibraltar quarry site was incorporated years later into a larger, modern aggregate quarry in the area. This would have erased any physical evidence of the historical quarry.

Even if the historical Gibraltar quarry’s stone was not used for monuments and decorative purposes, it was likely used as aggregate to build roads and infrastructure. Aggregate is the most-mined material in the world because it is used in virtually all infrastructure including homes, roads, schools and hospitals. Aggregate makes up about 80% of concrete and 94% of asphalt.

Building one kilometre of highway takes about 18,000 tons of aggregate - enough rock to fill four Olympic-sized swimming pools! Nova Scotia needs 10-15 million tons of new aggregate each year to build and maintain our infrastructure.