Welcome to my EarthCache! An EarthCache is a special type of geocache where there is no container to find – instead, you are looking for a unique geological feature of the area and need to answer questions, as well as posting a picture, in order to claim the find.
This EarthCache will take you to the Burford Fairgrounds in Burford, Ontario, where you will be examining a metamorphic rock known as schist. These rocks not only tell the story of the people and places that display them, but also of the ancient geological forces that shaped our planet long before human history began. You can find samples of schist all along the fence that surrounds the nearby memorial.
The schist seen here did not form locally. The bedrock beneath Burford is composed of flat-lying Paleozoic sedimentary rocks — primarily limestone, dolostone, and shale — that were deposited in warm, shallow seas around 400–450 million years ago. These rocks have never been buried deeply enough to experience the heat and pressure required to form schist. This means the rock you see here was transported from elsewhere, most likely from the Precambrian rocks of the Canadian Shield to the north, where some of the oldest and hardest rocks in North America are found.You can find rocks such as these in the wild in areas like Sudbury, North Bay and Parry Sound.
EARTHCACHE REQUIREMENTS
As with all of my EarthCaches, I am not looking for PhD thesis-level responses, but I do hope you take a few moments to make careful observations and learn something new. Please include a list of all cachers with your answer if answering for more than one caching name, but note that each cacher must upload their own photo to their log.
To claim a ‘find’ for this EarthCache, you must answer the following questions and send your answers in a message or email to the cache owner using the link at the top of the page. You may log your find immediately with your photo. I will be in contact if there is a problem, so there is no need to wait for a response before logging.
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Describe the stone: Observe the schist at the posted coordinates. Describe its texture and appearance. Is it smooth, rough, flaky, sparkly, or dull? Are the layers (foliation) easily visible? Can you see the mica flakes in the layers of these stones?
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Identify the colours: List at least two distinct colours that you can see (hint - look for the mica, and then at the surrounding stone). Based on the information in the description below, what minerals might be responsible for these colours?
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Identify the forces at work here: The layers (foliation) in schist form when minerals are forced to align under pressure. Do the mineral layers here appear straight, wavy, or crumpled? What might this tell you about the amount of deformation the rock experienced?
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Photo (mandatory): Include a photograph of yourself, your GPS, or a signature item with the schist visible in the background. You do not need to show your face, but the photo must be unique to you.
INTRODUCTION
Schist is a metamorphic rock — meaning it started out as another rock type that was transformed by heat, pressure, and chemically active fluids within the Earth. These transformations happen deep underground, usually during mountain-building events, when continental plates collide and push older rocks down into the hot, pressurized crust.
Schist typically forms from shale or mudstone, which are fine-grained sedimentary rocks made of compacted clay. As these rocks are buried deeper, the clay minerals begin to recrystallize and realign into mica — a shiny, sheet-like mineral that gives schist its sparkle.
If metamorphism continues, the rock may eventually form gneiss, which displays distinct light and dark mineral banding. Schist represents an intermediate grade of metamorphism, where minerals are large enough to see, but the rock has not yet developed the strong compositional banding of gneiss.
HOW SCHIST FORMS
The formation of schist involves several stages of increasing metamorphism:
Each stage reflects increasing temperature and pressure.
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Shale forms at the surface from compacted clay.
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Slate develops when shale is buried deeper, forming a dense, fine-grained rock that splits easily.
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Phyllite forms as the minerals begin to grow and give a silky sheen to the rock.
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Schist appears when the minerals — especially mica — grow large enough to be visible to the naked eye and align in shimmering, foliated layers.
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Gneiss forms under even higher temperatures, where minerals begin to separate into distinct light and dark bands.
In schist, the pressure causes flat minerals like muscovite and biotite mica to line up parallel to each other, creating the foliation (layering) that defines the rock’s texture.
Over time, additional minerals such as garnet, staurolite, chlorite, feldspar, or quartz may grow within the rock, giving it colour and sparkle. These minerals act as metamorphic “thermometers,” revealing the temperature and pressure conditions under which the rock formed.
COLOUR VARIATIONS IN SCHIST – WHAT THEY MEAN
The colours seen in schist reflect its mineral composition, which depends on the parent rock and the exact conditions of metamorphism.
Silvery Grey:
Produced by muscovite mica, a light, reflective mineral that forms from aluminum-rich clay minerals.
Bronze or Golden Brown:
Caused by biotite mica, an iron- and magnesium-bearing mineral that forms under higher temperatures than muscovite.
Green:
Results from chlorite, actinolite, or epidote, which form when mafic (magnesium- and iron-rich) rocks like basalt undergo metamorphism. Rocks dominated by these minerals are often called greenschist.
Reddish or Pink:
May be due to garnet crystals (commonly almandine garnet) or iron oxidation along cracks and cleavage planes.
Dark Grey or Black:
Comes from large amounts of biotite, graphite, or amphibole. Graphite-rich schist, derived from carbon-rich shale, can have a greasy or metallic sheen.
Blue or Steel Grey:
Rarely, a blue tint comes from glaucophane, a mineral that forms under high-pressure, low-temperature conditions typical of subduction zones.
Each of these colours records specific geological conditions — a chemical fingerprint of the temperature, pressure, and parent rock type at the time of metamorphism.
WHAT SCHIST TELLS US
Schist is a record of the immense forces that act within our planet. Its shiny, foliated layers formed miles underground during episodes of mountain-building and tectonic compression. Each flake of mica represents countless years of mineral growth under stress.
By examining schist, geologists can determine:
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How deep the rock was buried,
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What temperature and pressure it experienced, and
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What type of rock it originally was.
Although schist is now found at the surface, it once lay deep within the roots of ancient mountains — proof of the dynamic processes that have shaped North America over billions of years.
AI Content Disclosure
Some of the descriptive text and/or images on this page were created with the assistance of artificial intelligence tools. All information has been reviewed, verified, and edited by the cache owner for accuracy and clarity.
This cache was placed by a PROUD Platinum EarthCache Master.
