Marble is a metamorphic rock formed when sedimentary limestone is exposed to high temperatures and pressures.


Photo by Brent Eades.

Display rock 1 is metamorphic marble of Precambrian age from the Canadian Shield of Lanark County. 

About a billion years ago our part of the world was much smaller than the present day continent of North America.  Off the coast, to the east, were microcontinents of volcanic islands with intervening seas and sedimentary basins.  A modern example might be Indonesia with its many volcanic islands.

The westward moving microcontinents collided with the mainland, one after the other.  The repeated collisions thrust the volcanic and sedimentary rocks up and over the continental edge.  The thrust sheets of the separate landmasses were pushed together, folded, buckled, invaded by magma, and pushed skyward to form the Grenville Mountains along the eastern coast of the continent.  A modern example is the Himalaya Mountains formed by India colliding with Asia.

Deep within the roots of the Grenville Mountains, the volcanic and sedimentary rocks of the microcontinents were transformed into metamorphic rocks.  Limestone was changed to marble.


Public domain image by G. Mills via Wikimedia Commons.

The ancient roots of the Grenville Mountains extend across North America from Labrador to Mexico.

The transformation from limestone to marble involved tremendous pressures and temperatures. This sample is from the marble quarry of OMYA Canada Inc. near Tatlock, about 30 km west of Almonte in Lanark County.  The marble is of Precambrian age, about a billion years old, part of the geological Grenville Province of the Canadian Shield.

Unlike the smooth and massive marble used in kitchen floors and countertops, the Tatlock quarry marble is medium to coarse grained.  It’s a high purity marble, and the calcite crystals are not well cemented.  Pure calcium carbonate is produced from the quarried marble and used as a filler in other products, such as paper, plastics, paints, and coatings.

Roy Specimen 1 Photo December 3 2016

Photo by Roy Bassoo.

If you look closely, there are also small specks of the metallic minerals hematite, Fe2O3, and pyrite, FeS2, in display rock 1.

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