When visiting Lake Champlain keep an eye out for striking iberville shale, limestone, marble, dolostone, slate and magnetite. The stones here are unique as they were formed by heat and pressure of tectonic movement.
The fault has created two mountain ranges and very unique rocks.
Geology is at the center of the attraction of Lake Champlain and rock lovers will find themselves in good company.
Types of Rocks at Lake Champlain
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The most striking rocks to find at Lake Champlain are Iberville Shale. These gray stones with white banding were first recorded in Iberville in Quebec.
These sedimentary stones were formed with white calcite bands making patterns across the surface of the rocks.
Many samples that are collected have been tumbled in the lake or the seas the preceded the lake.
Read more about Iberville Shale in this article.
Before the glaciers retreated Lake Champlain was home to sea life and corals.
As these marine animals die their calcium skeletons leave large amounts of calcium carbonate on the seafloor.
The calcium carbonate compacts down into sedimentary limestone.
Limestone can be identified by its relatively soft texture, it has a hardness of 2 to 4.
If you look closely limestone has a fine texture and it can usually be scratched with the point of a knife. It was also effervese in an acid test.
Fossils are commonly found in limestone and at Lake Champlain there are some important fossils.
There is a unique fossil record of what is believed to be the earliest corals. These corals are the ancestors of coals found in today’s oceans.
The fossil record here shows the evolution of coral formations over time. There are examples of many types of corals and incredibly ancient corals.
The limestone containing the fossils is dark gray to black, an unusual color for limestone.
The Chazy Fossil Reef can be seen in several locations within lake Champlain. Three islands: Isle Le Motte, Valcor Island and Garden Island.
Dolostone is formed in the ocean like limestone, but the calcite in the stone has been replaced with dolomite.
This results in a rock with a high level of magnesium. The magnesium and calcium in dolostone is called dolomite.
Like limestone it is a fine grained sedimentary rock. It is the same color as limestone; white, light brown and gray.
Dolostone is resistant to erosion and forms the large stones that can be seen along the coast of Lake Champlain.
The shale and limestone surrounding the dolostone will wear away much quicker leaving a special type of karst landscape.
This exists because the older dolostone was pushed up in the thrust formation and the younger shale was thrust beneath it.
The limestone that was once plentiful in Lake Champlain was forced together by tectonic action and metamorphosed into marble.
Marble is a very fine grained rock that ranges in color from white to black. At Lake Champlain black marble is present in large quantities.
The rock forms Marble Island in Lake Champlain.
There is a Marble Museum dedicated to the marble industry that thrived in the area beginning in 1880. Proctor Vermont
Shale that has been heated under pressure becomes slate. In the Slate Valley on the border of Vermont and New York there is a large deposit of slate.
The slate was formed when the two tectonic plates collided. This collision formed the Appalachian mountains and formed many of the area’s unique stone deposits.
The slate here was quarried for use as shingles. The mining in the area began in the 1850s.
When visiting Lake Champlain you can learn more by visiting the Slate Valley Museum.
Anorthosite is formed deep in the earth when magma gets close to the surface and then cools slowly. This results in a coarse grained stone that is not well understood.
The largest deposit of anorthosite is in the Appalachian mountains. It makes up the foundation of the Adirondack High Peaks region.
Anorthosite is less dense than magma meaning that it must be made up of rocks that floated to the surface of the magma when it was pushed to the surface.
Magnetite is an iron ore that has magnetic properties. Magnetite is a smooth crystal that is gray to black or it may be a gray to black dust.
It is often mined for it’s iron content and is also used today to help measure and map underground rock formations.
The iron mined around Lake Champlain was used during American war efforts and for construction of railroads.
Geologists can use tools to measure the magnetism of the stone to see under the surface of rock formations.
It is believed to help guide salmon and other marine life in their migration patterns as the salmon respond to the magnetic field produced by these minerals.
It is found in and around Port Henry, NY where you can learn more about the iron industry in the area at the Iron Center Museum.
Stories in Stone Program
When visiting Lake Champlain be sure to check out the Stories in Stone program in Shelburne Farm in Vermont.
This family friendly guided program that discusses the geological history of Lake Champlain and guides you to coastlines where you can find your own Iberville Shale samples.
The program has rotating themes, so check to see what the current offerings are on their website.
Rocks at Lake Champlain
The unique geology of Lake Champlain is one of the major reasons for visiting the area. There are many attractions that revolve around the geology of the region.
See fossils, learn mining history and search for exciting samples of rocks at Lake Champlain.
Be sure to take some time to search for the famous Iberville Shale.
Obey all posted signage when collecting or removing any rocks. Many of the areas around the lake are National Monuments or protected areas where policies may be strict.
Consider supporting the local economy by purchasing local stones and raw samples at some of the many rock shops in the area:
The Crystal Cottage of Vermont
Gem Goddess Emporium
The Hidden Gem (Plattsburg, NY)
Spirit Dancer Crystals and Gifts
These shops are great places to learn more about local rocks and gems.
Carry With You
If you are planning a hike where there will be rocks to pick through, consider packing one of the following:
- National Audubon Society Field Guide to Rocks and Minerals (small book with pretty colored pictures to help identification)
- National Audubon Society Field Guide To North American Fossils (small book with pictures)
- Gemstone & Crystals Properties (durable fold-up guide)
- Small UV Flashlight
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