Jersey Island Geopark I
A Geopark is about more than rocks
Jersey is a strong contender for this special designation because of our Island's exceptional geology and our important cultural heritage which forms the outstanding surroundings we enjoy every day. Whether exploring Jersey's diverse landscapes or seascapes there is lots to discover and inspire you.
Summer opening hours: March to October - 10am to 5pm
Winter opening hours: November to February - 10am to 4pm
Closed: 24, 25, 26 & 31 December and 1 January
To log this Earthcache, visit the Jersey Island Geopark and answer the following questions.
You can find 7 Jersey rocks in the Jersey Island Geopark, answer questions about 4 stones.
1. Flow-banded rhyolite Examine the stone and describe the distinctive bands (width and number). Can you see any flattening of the crystals?
2. Diorite formed from gabbro and granite: Please describe the rock, including the size and color of the crystals. What rocks are the different crystals made of?
3. Particular Granite: What shape, size, and colour are the crystals in this granite?
4: Rhyolite with spherulite: How thick is this vein of calcite and what is the surface texture?
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You don't have to wait for permission to log, if the answers are wrong I will contact you, without answers your log will be deleted.
1: Flow-banded rhyolite
Flow-banded rhyolite is a high-silica, extrusive volcanic rock with a distinctive streaky or swirling pattern caused by the slow, viscous flow of magma that deforms crystals and glassy material within the flow. These bands can vary in color or granule size and are a result of friction, the flattening of glassy shards and pumice, and variations in the magma's volatile content. The rock is formed in continental arc settings, and its banded appearance is a visual record of the complex flow dynamics and cooling history of the lava flow.
2: Diorite formed from gabbro and granite
Diorite does not form from gabbro and granite, but rather is a rock that is intermediate in composition between them. It forms when magma that is less silica-rich than granite and more silica-rich than gabbro cools slowly underground. The resulting diorite rock has a characteristic "salt and pepper" appearance, a result of its light-colored plagioclase feldspar and dark-colored minerals like hornblende or pyroxene.
3: Particular Granite
"Granite" refers to a rock with diverse properties, while "granitoid" encompasses a broader class of rocks that includes granite, but also other igneous and metamorphic rocks, such as gneiss or syenite. Granite itself is an igneous plutonite composed primarily of quartz and feldspar, formed by the slow cooling of magma. Different granite species differ in their precise mineral composition and color, making them attractive for decorative and functional uses such as countertops, flooring, and paving.
4: Rhyolite with spherulite
Rhyolite with spherulites, or spherulitic rhyolite, is a volcanic rock formed from glassy, silica-rich lava that has undergone devitrification, a process where the glass crystallizes into round, ball-like structures called spherulites. These spherulites consist of radiating, fibrouscrystals, typically quartz or feldspar. The presence of spherulites indicates that the lava cooled very quickly, trapping a glassy matrix before minerals could form in their normal crystalline structures.
Picture:
from Jersey Island Geopark
Sources:
from Jersey Island Geopark
1: www.usgs.gov/observatories/yvo/news/rock-glass-and-flowbands-yellowstones-rhyolite-anatomy
2: en.wikipedia.org/wiki/Diorite#:~:text=Diorite%20(%2Fˈdaɪ.,-silica%20(felsic)%20granite.
3: www.planolith.de/en/production/material/#:~:text=Natural%20granite%20is%20an%20alkaline,for%20and%20degreasing%20the%20stone.
4: www.usgs.gov/observatories/calvo/news/getting-sphere-ious-about-