Iberville shale is both a sedimentary rock formation and a beach stone named after the former town of Iberville in southern Quebec.
More widely recognized as a beach stone, Iberville is marbled with white, crystalline veins running across and through each individual rock in unique and varied patterns.
So, what makes this particular shale worth our time and attention?
Iberville Shale: Identification, Uses, and Meaning
Origins of Iberville Shale
To begin, Iberville shale is primeval, pre-dating the first mass extinction event, known as the Ordovician Extinction.
The fact that we can hold a rock in our hands that passed through five extinction events is mind-numbing.
About 480 million years ago, North America was mostly underwater, and the seas were filled with invertebrate animals such as trilobites and mollusks.
At the same time, the sediment that would become Iberville shale began to consolidate.
Blankets of debris containing particles of silt, clay, and dead marine life settled onto the ocean floor.
Over millions of years, the particles were compressed, compacted, and cemented in the process of lithification to form shale.
The result was the sedimentary layer of the Lake Champlain Thrust Fault.
Over time, this layer of shale rose to the surface from the sea floor by forces of erosion and became the unique shale we now call Iberville.
Covering the shores of Lake Champlain, the signature beach stones are a hallmark of the region, which is bounded in the east by New York, in the west by Vermont and by the town of Iberville at the lake’s northern tip (Iberville merged with Saint-Jean-sur-Richelieu in 2001).
But what about those unusual white streaks?
Iberville shale’s microscopic particles were cemented together with a coating of calcite (calcium carbonate or CaCO3), derived from the shells of dead marine life – recall those trilobites and mollusks?
Since it’s poorly soluble, calcite precipitates from super-saturated water (picture stalactites and stalagmites).
Calcite is the cement that binds the sediment and composes the crystalline veins that make Iberville shale distinctive.
Different from the process of cementation, the veins crystallized from liquefied calcite that was forced between the fissures of the coalescing shale.
Typical for a shale, Iberville is dark gray and flattened.
A fine-grained sedimentary rock, it feels smooth.
On the Moh’s scale of hardness, it’s about a 2 or 3 (for context, diamond is the hardest mineral at 10).
Keep in mind that the scale is a measure of mineral hardness and shale is not a pure mineral.
The size and shape of the individual stones vary widely.
Unusual for shale, networks of white streaks mark the surface.
Where Are These Stones Found?
Found along the shores of Lake Champlain, the Iberville stones have a softly polished look and feel.
We could spend days rummaging through countless stones without finding any duplicates.
Each rock has its own personality, from boldly striped rectangles to whimsically filigreed heart shapes.
Iberville shale is found only in the Lake Champlain Valley and is unique in its specific ingredients and rock-forming or lithification process.
The rocks and landforms of the valley are a geological wonder, making it a beautiful place to vacation and rockhound.
Most notable is the Lake Champlain Fault Thrust , as previously mentioned.
It’s made of dolostone (a sedimentary rock like limestone) and the dark gray shale layer known as the Middle Ordovician Iberville Formation.
It is a reverse fault, meaning that the older dolostone is on top of the younger Iberville shale.
About 450 million years ago, geologic forces caused Maine to push into New Hampshire, which in turn pushed into Vermont, forming the Green Mountains and uplifting the Lake Champlain Fault (among other faults in the region).
The region is also home to the world’s oldest fossil coral reef and the site of a 10,000-year-old beluga whale.
Bordered by Vermont’s Green Mountains and New York’s Adirondacks, Lake Champlain is about 120 miles long.
Visiting any of the beaches around the lake, we can easily recognize the flat, dark gray beach stones, crisscrossed with white stripes, named Iberville – a remnant of the valley’s ancient geologic past.
We’ll see other gray beach stones with streaks or bands, but we can recognize Iberville because it’s flatter, and has the characteristic white streaking.
Uses of Iberville Shale
Unlike other types of shale which are used to make pottery, tile or cement, Iberville doesn’t have a large scale commercial use.
So, by definition, it’s not a ‘natural stone’, which refers to building or architectural stones that are quarried from the earth.
For example: granite, marble or slate (a metamorphic rock derived from shale).
It’s more of a decorative stone with interesting shapes and patterns.
After querying ‘Iberville shale,’ we found unique jewelry pieces for sale on Etsy and dozens of images.
For the creatively inclined person, the endless variety of sizes, shapes and patterns spark the imagination, and we thought of a few crafting projects using Iberville beach rock.
The fact that the stones are flat, soft, smooth and of varying shapes and sizes makes them an excellent medium for crafting.
As an example, we could build small cairns by stacking the stones, or use the stones as borders to enhance a garden or walkway.
We could also fill a clear glass bowl or vase to create centerpieces and flower arrangements.
A Wishing Stone
If you find an Iberville rock with an unbroken ring or stripe around it, you’ve identified a legendary ‘wishing stone.’
Make a wish by tracing the ring with a fingertip.
You can wish for yourself, but if you wish for someone else, their wish and yours may come true.
Like the legend of the four-leaf clover, such a stone would be a rare find and would involve hours of sorting through countless beach stones – well worth the effort of a true believer.
Iberville shale isn’t a precious or semi-precious stone, but we think it’s rare since it’s only found in Lake Champlain Valley.
And since no two beach stones are the same, it’s definitely collectible.
Ultimately, value – like beauty – is in the eye of the collector and worthy of our time and attention.
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