March 22. Vermont marble

As we approach the end of March, we’re getting later and later in the Ordovician, and the collisions along the east coast of North America are getting more and more intense. We’re building up to the Taconic Orogeny, and yesterday we talked about one of the consequences of that mountain-building event, the eroded sediment that created the Queenston Delta.

Rutland marble quarry

Closer to the action, where blocks of continental crust, piles of volcanic rocks, slices of oceanic crust, and whatever else was out there were actually colliding to raise up those mountains, things got pretty hot and heavy. All those nice tropical shallow seas earlier in the Ordovician made nice limestones. But when you put a limestone under high pressure and add some heat, the calcite crystals in it recrystallize – it’s still calcite, but instead of gently interlocking and usually tiny crystals, they grow and intergrow more tightly, producing a metamorphic rock called marble.

Some of the best marble in the United States was created during the Taconic Orogeny, cooking those nice Ordovician limestones. Especially in Vermont, but also in Tennessee and Georgia, Ordovician marbles have been mined for centuries as building stone and for monuments. The Amphitheater of Arlington National Cemetery is made of Ordovician Vermont marble – one of a great many structures that are. The quarries near Rutland, Vermont, yield white marble, but with plenty of variations in the original limestone, you can get all sorts of colors in marble, from red to black. The oldest marble quarry in Vermont, at Isle la Motte, was opened by Ichabod Fisk in 1664. Vermont quarries also produce verde antique, a metamorphic rock containing green serpentine and similar minerals, used for countertops, tiles, and facades.

* * *

Today, March 22, is the birthday of Adam Sedgwick. You must remember him, the geologist who defined the Cambrian and lost a friend over the details of Cambrian-Silurian stratigraphy. He was born March 22, 1785, in Dent’s Town, Yorkshire, England.

—Richard I. Gibson

Photo by C.W. Nichols, Rutland, VT marble quarry c. 1870. Public domain, via NY Public Library and Wikipedia.

Reference
Vermont Marble Industry