Scotch Lake

The Scotch Lake Dolomite Quarry in Cape Breton (aka the Georges River Quarry) operated from 1899-1951 and was owned by the Dominion Iron and Steel Company (acronym: DISCO!).

DISCO made steel with Cape Breton coal and iron from Newfoundland in Sydney's Whitney Pier neighbourhood (named for Henry Melville Whitney, DISCO's president). Steel is iron and carbon, and the carbon is derived from coal.

DISCO used the Scotch Lake Quarry dolomite as flux in its steel mill. Flux is used in the smelting process to promote fluidity and remove impurities in the form of slag. Dolomite has many other uses, including as acid neutralization in the chemical industry, in stream restoration projects and as a soil conditioner.

In 1911, the quarry was sending 300 tons of rock a day via rail to Sydney. It employed 65 men. Hand drills and dynamite were used to extract the rock.

The quarry, which was cut into the Boisdale Hills, was also used for construction aggregate in the 1960s.

In addition to dolomite, the quarry also contains limestone, marble and serpentine. Marble and dolomite are both metamorphosed limestone – they started as limestone but were turned into different rocks. Dolomite is limestone that has been chemically modified by magnesium-rich groundwater.

Marble is pure limestone that was subjected to extreme heat and pressure which turned it into marble. By “pure” we mean the limestone was essentially pure calcium carbonate and did not contain a lot of impurities like quartz, clay, feldspar, micas, etc.

If the limestone is impure, the various minerals chemically interact with each other during the heat and pressure of metamorphism and form a whole host of other minerals.

That is what happened with the rock pictured below, which is from the Scotch Lake Quarry. It is serpentinized marble, meaning the mineral serpentine was produced as the limestone was turning into marble, and the marble and serpentine intermingled.

If this sounds confusing, think of it this way: If you put a potato in boiling water you simply end up with a boiled potato. If you add carrots, turnips, meat, salt, pepper, all these things interact with the potato and each other to form a stew.

In this analogy, marble from pure limestone is the potato. One thing, nice and simple.
The serpentinized marble in the picture is stew – a bunch of minerals interacted chemically during the formation process and produced a complex mixture of rocks in the quarry. (Geology is often a complex, messy business!)

There is quite a lot of serpentine at the Scotch Lake Quarry.

Serpentine comes in a variety of colours, including yellow, green, olive, blue and red. The serpentine in the picture clearly has a lot of yellow with hints of green.

The red is likely a coating of hematite on the sepentinized marble. Hematite is a mineral that contains iron that has oxidized/rusted, giving it the red colour.