Welcome to This EarthCache
An EarthCache is a special type of geocache with no physical container. Instead, you are exploring a unique geological feature — in this case, granite with a rare blue or opalized sheen — and observing the natural processes and minerals that give it its distinctive appearance. This large and striking monumnet, in memory of Mary Jane Evans and John C Evans, contains a unique blue pigment that causes a shimmering effect within this stone monument. This earthcache will highlight the unique blue appearance of this stone and help you to identify it.
As with all of my EarthCaches, I am not looking for PhD-level answers. Take the time to observe carefully, think about what you see, and learn something new about the geological history of the area. If you are visiting as a team, please include all caching names in your submission.
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.
Logging Tasks
1. Observation: Examine the granite at the site. Do you notice any blue or opal-like sheen? Where does it appear—within individual crystals, along fractures, or across larger surfaces?
2. Mineral Identification: Based on your observations, which mineral(s) might be responsible for the blue coloration? Consider options such as labradorite, kyanite, blue quartz, or altered dark minerals. Explain your reasoning.
3. Surface Characteristics: How does the granite’s texture—including grain size, layering, or twinning—affect the way it reflects light?
4. Photo Requirement: Take a photo showing that you visited the site. This can include yourself, your GPS device, your geocaching username on paper, or another signature item, with the monument in the background. You do not need to show your face, but each geocacher should upload an image with their log to verify their visit.
Earthcache Lesson:
Granite and Its Colors
Granite is a coarse-grained igneous rock made primarily of quartz, feldspar, and mica. While it is commonly white, grey, pink, or black, some granite displays unusual colors, including blue or opalescent sheens.
This blue coloration can result from several factors:
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Labradorite (a type of feldspar): Labradorite is a feldspar mineral that can produce a striking blue iridescence, called labradorescence. This effect occurs because of thin, parallel layers or lamellae within the crystal that refract and reflect light at specific angles. Labradorite forms during the slow cooling of magma in igneous rocks such as granite or gabbro. It is typically found in igneous intrusions and layered mafic rocks, and in some cases, in metamorphic rocks derived from igneous protoliths. The largest and most famous deposits of labradorite are found in Labrador, Canada (which gives the mineral its name), as well as in Finland (spectrolite), Madagascar, and parts of Norway. Labradorite can appear in colors ranging from blue to green, yellow, and even reddish-orange, depending on the crystal structure and angle of light.
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Kyanite: Rarely, bladed crystals of kyanite appear as subtle blue streaks.
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Blue quartz or silica inclusions: Tiny inclusions or veinlets of hydrothermal silica can scatter light to create an opalescent effect.
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Alteration of dark minerals: Weathering or oxidation of amphiboles or pyroxenes can impart a bluish tint to darker granites.
The combination of mineral composition, crystal orientation, and light reflection creates the shimmering or opalized appearance that makes this granite visually striking.
Formation of Blue Sheen in Granite
Blue sheen granite forms through a combination of igneous crystallization and secondary mineral processes:
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Primary crystallization: Slow cooling of magma allows feldspar and quartz crystals to grow large enough to interact with light.
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Layering or twinning in labradorite: Parallel layers within feldspar crystals refract and reflect light, producing the characteristic blue labradorescence. The degree of labradorescence depends on the thickness of the layers and the crystal orientation.
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Hydrothermal alteration: Mineral-rich fluids can deposit silica or other minerals in fractures, contributing opalescent colors
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Weathering: Chemical alteration or oxidation of dark minerals over time can enhance the blue effect.
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Geological Significance
Observing blue or opalized granite provides insight into:
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The mineralogical composition of the rock, including feldspar, quartz, and silica inclusions.
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Igneous processes such as slow crystallization and crystal alignment.
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Secondary geological processes, including hydrothermal mineral deposition and weathering.
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The formation and occurrence of labradorite, which reflects specific crystallographic layering and contributes to iridescence.
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Light interactions in minerals, explaining the shimmering or opalescent appearance.
Labradorite, in particular, is significant for its unique optical properties, global distribution in igneous rocks, and its use as a decorative stone and in jewelry. Its presence in granite adds both visual appeal and scientific interest, revealing the history of the rock’s formation and the interplay of light with mineral structures.
About this area:
Howitt Memorial Cemetery, located at the intersection of Sideroad 10 N and Laird Road W in Puslinch Township, Wellington County, is a quietly maintained, inactive cemetery near the Waterloo Region boundary.
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.
