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 takes you to Eastlawn Cemetery in Hamilton, where you are looking for a large monument for the WILGOSH family. This striking stone has a very unique look, vastly different from other granite stones surrounding it - this is because it is actually make up to two different types of granite, that have been banded together in layers. Unlike gneiss, this banded rock is not twisted and gnarled to make a different pattern - the granites are in very distinct and almost straight layers that gives us clues into how this granite was formed millions of years ago.
EARTHCACHE REQUIREMENTS
As with all of my ECs, I am not looking for PhD thesis level responses, but I am hoping that you take some time to enjoy the area and learn something new. Please include a list of all cachers with your answer, if answering for more than one caching name. There is no need to send individual answers.
To claim a 'find' for this Earthcache you must answer the following questions and send your answers in a message or email to the owner using the link at the top of the page. You can log your find with a photo at GZ. Send your answers to the tasks. I will be in contact if there is a problem, no need to wait for a response as long as the required photo is included in your log.
Observational Task
At GZ, you should be standing in front of a large striped monument for the Wilgosh family. You can make your observations from either side of this monument.
Questions to Answer:
To claim this EarthCache, please visit the posted coordinates and examine the granite exposure carefully. Then answer the following questions:
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Describe the bands you see. Are they mostly straight or wavy? Are they thick or thin? That is the width of the thickest band you see, and what is the width of the thinnest bands you see? How many different colors of bands can you count?
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Color Contrast: Choose one light band and one dark band. Describe their texture (grain size, mineral visibility) and speculate on what minerals are causing the color difference. Which colour has the larger crystals and which has a more sparkly appearance?
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Interpretation: Based on what you observe, which process do you think most likely caused the banding at this site (fractional crystallization, magma mixing, or flow banding)? What evidence supports your idea?
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Photo: Include a photograph of yourself, your GPS, a signature item, thumbs up, etc with the monument in the background. You do not need to show your face in the photo, but your photo must be unique to you. In the event of group photos, please have each member of your group upload the photo (each log should have at least one photo uploaded).
Earth Science Lesson
Granite is typically thought of as a uniform, speckled rock – but sometimes, nature leaves behind a much more dramatic record. At this site, you'll see distinct bands or layers of granite, forming straight lines or sinuous waves. These layers record a fascinating story of deep crustal processes, magma mixing, and tectonic forces. Let's explore what you're seeing and how it formed.
What Is Granite?
Granite is a coarse-grained igneous rock that forms when magma cools slowly deep underground. It’s made up mostly of quartz, feldspar, and mica, which give it a speckled appearance with colors ranging from pink and white to grey and black. Because it cools slowly, the crystals have time to grow large enough to see with the naked eye. Granite is very hard and durable, which makes it a popular material for buildings, monuments, and gravestones.
But not all granite is uniform. When conditions change during its formation, it can develop layered or banded structures that preserve those shifting environments.
What Causes the Layering in Granite?
The layering you see here is known as magmatic foliation. There are several possible causes:
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Fractional Crystallization - As magma cools, different minerals crystallize at different temperatures. Layers can form as early-crystallizing minerals settle out first, forming light or dark bands depending on composition.
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Magma Mixing - If a second pulse of magma intrudes into the same body but has a slightly different composition, it can mix imperfectly with the original melt. This creates bands of contrasting mineral content and color.
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Mineral Zoning - Granite forms in large bodies (plutons), and as magma cools, it crystallizes in layers based on mineral density and composition. Lighter-colored minerals (like feldspar and quartz) and darker ones (like biotite and hornblende) can segregate into bands over time. If a monument slab is cut across these layers, the contrast becomes especially vivid.
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Flow Banding - During the final stages of cooling in a granitic magma chamber, minerals begin to crystallize and align in the direction of magma flow. This creates stripes or streaks of color that resemble the swirling of taffy. These are subtle in the raw rock, but when the slab is cut parallel or perpendicular to the flow direction, these layers become much more visible—especially after polishing.
Why Are the Layers Different Colors?
The colors in the bands come from the different minerals present. Light-colored bands are rich in feldspar and quartz, which are light in color. Dark-colored bands contain more biotite or hornblende, which are rich in iron and magnesium. This color contrast reflects chemical variation in the magma or the order in which minerals crystallized.
Why Are Some Layers Wavy Instead of Straight?
In many places, the bands are slightly curved - not in the severe folds typically associated with gneiss, but instead into slight waves. This is due to deformation during or after the granite crystallized. The Earth's crust is not static; it’s constantly moving. Tectonic pressure can deform even solid rock. If the granite was still partially molten or soft during this time, it could be bent like clay – preserving those flow folds as it solidified.
What Makes This Granite Unique?
Most granite is massive and unlayered. This banded granite is unusual because it preserves Multiple stages of intrusion or crystallization, textural and mineralogical zoning and evidence of tectonic forces operating deep underground
These characteristics make it closer in appearance to migmatite or gneiss, but it retains its igneous origins. The sharp layers and contrasting mineral bands are a snapshot of complex processes inside the Earth’s crust.
Resources:
Natural Stone Institute
https://www.naturalstoneinstitute.org
“Rocks and Minerals of the Earth”
https://www.usgs.gov/faqs/what-are-igneous-metamorphic-and-sedimentary-rocks
Mindat.org – Granite Mineral and Rock Database
https://www.mindat.org