A Guide to Cork City's Geological Heritage

Blackrock Diamond Quarry Located between Monahan Road and Blackrock Road is a location with a name that could make any assuming rock enthusiast fly out with a digger and a hammer! However, the same rock capitalist will be sorely disappointed after spending hours of quarrying for rare precious gemstones as there are no diamonds in Blackrock Diamond Quarry. But there is a reason why it is referred to as such.

Amethysts are very different from diamonds. Though they are both considered gemstones, amethysts are a purple variant of the mineral quartz. Quartz is one of the most common minerals on the surface of our planet, while diamonds are an extremely rare, crystallised form of carbon. Except for the occasional crystal healer and rock admirer, amethysts don’t pose much economic value. That doesn’t mean that it isn’t worth looking at.

Beautiful limestone outcrop at The Black Market Cork along Monahan Road.

Back when it was part of Cork City’s productive rock extraction industries, limestone blocks were extracted from this area, likely to be used for construction and agriculture. Some of these limestones had cracks and pockets where mineral-rich waters could flow through. These minerals accumulated in these pockets as the fluids themselves disappeared. Over time, large crystals grew into these pockets and in particular the mineral amethyst, which prompted the name ‘Blackrock Diamond Quarry’.

The quarry is today inactive and the location of an industrial park along Monahan Road and therefore not accessible to the public. That being said, it is of an impressive size and observing it from the road is in itself interesting. Above the tall walls of the quarry, it is possible to see the obelisk McCarthy’s Monument with its limestone bricks towering at Blackrock Road. The quarry walls can be accessed through the Black Market Cork, where the white crinoidal limestone outcrop can be studied in close-up.

Stunning, but not a diamond!

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