Very Scilly Pebbles at Porth Hellick EarthCache

This is an earth cache. There is no container at the published coordinates. You will have to send me the answers to the questions in the description within twenty four hours of logging this earth cache or your log will be deleted. Happy caching!
 

Welcome to Porth Hellick Beach on St. Mary's, Isles of Scilly! This EarthCache will take you on a geological journey to explore the fascinating granite pebbles found on this beautiful shoreline. Porth Hellick Beach is a unique location to study the rock formations, uncovering the ancient history of this region. Let's dive into the geological marvels of these granite pebbles and discover the story they have to tell.

Geology and Formation: The Isles of Scilly are a group of stunning islands located off the southwestern tip of Cornwall, United Kingdom. The geology of the islands is primarily composed of granite, which was formed during the Variscan Orogeny, a major mountain-building event that occurred during the late Paleozoic era, around 300 million years ago.

The granite found at Porth Hellick Beach originated from a vast molten magma chamber deep within the Earth's crust. Over millions of years, this magma slowly cooled and solidified, forming a coarse-grained igneous rock known as granite. As the Earth's surface eroded over time, the granite was exposed and gradually broke down into smaller fragments, eventually forming the pebbles we find on the beach today.

Pebble Shapes and Sizes: Take a close look at the granite pebbles on the beach. You'll notice that they come in various shapes and sizes, ranging from smooth and rounded to angular and irregular. These variations in pebble shapes are a result of the different geological processes they experienced during their journey from the original granite outcrops to the beach.

The round and smooth pebbles were likely shaped through abrasion in rivers or streams, where they were transported over long distances, colliding with other rocks and sediment, gradually wearing away their edges. On the other hand, the more angular and irregular pebbles might have undergone minimal transportation, likely originating from nearby rockfalls or landslides.

Mineral Composition: Granite is primarily composed of three main minerals: feldspar, quartz, and mica. These minerals give granite its characteristic appearance and provide valuable insights into the rock's origin and history.

1. Feldspar: Look for small, rectangular-shaped crystals with different colors, such as white, pink, or gray. These are feldspar minerals, the most common being orthoclase and plagioclase feldspar.

2. Quartz: Notice the translucent or clear crystals that often have a hexagonal shape. These are quartz crystals, a hard and durable mineral that is a significant component of granite.

3. Mica: If you find thin, shiny flakes in the pebbles, these are mica minerals. Mica, either biotite or muscovite, provides a sparkling appearance to the granite.

Conservation Note: Porth Hellick Beach is a unique and sensitive geological site. As you explore the granite pebbles and admire the natural beauty of the area, please remember to follow the principles of Leave No Trace. Avoid removing or disturbing any rocks or pebbles, as they play an essential role in preserving the delicate balance of this coastal ecosystem.

Sources:

• Geology of the Isles of Scilly. (n.d.). Cornwall Wildlife Trust.
• Variscan Orogeny. (n.d.). Encyclopedia Britannica.

Logging Requirements: To log this EarthCache, please send me answers to the following questions:

1. Describe the shapes and sizes of the granite pebbles you observed on Porth Hellick Beach.
2. Identify at least two minerals present in the granite pebbles and describe their characteristics.
3. (Optional) Add a photo of you, your gps device or something with your geocaching username in your log. Make sure to have the beach in the background!

Note: You don't need to include the answers in your log, just send them to me directly through the messaging system or email me at 'euan.morris@yahoo.com'. Happy exploring!

Keywords with Definitions:

1. Granite: Granite is a coarse-grained igneous rock composed of minerals like feldspar, quartz, and mica. It forms from the slow cooling and solidification of molten magma deep within the Earth's crust.

2. Pebbles: Pebbles are small, rounded stones typically found on beaches or in riverbeds. They are created through the erosion and weathering of larger rocks.

3. Geology: Geology is the scientific study of the Earth's structure, composition, and processes, including the formation of rocks, minerals, and landscapes.

4. Igneous Rock: Igneous rocks are formed from the solidification of magma or lava. Granite is an example of a common igneous rock.

5. Minerals: Minerals are naturally occurring, inorganic substances with a specific chemical composition and atomic structure. They are the building blocks of rocks.

6. Feldspar: Feldspar is a group of minerals that are the most abundant in the Earth's crust. They have a variety of colors and are an essential component of granite.

7. Quartz: Quartz is a common mineral found in many rocks, including granite. It has a hexagonal crystal structure and often appears as clear or translucent crystals.

8. Mica: Mica is a group of shiny, sheet-like minerals that are often found in granite. Biotite and muscovite are the two most common types of mica.

9. Erosion: Erosion is the process of wearing away or displacing rocks and soil by natural forces such as water, wind, or ice.

10. Variscan Orogeny: The Variscan Orogeny was a major mountain-building event during the late Paleozoic era, around 300 million years ago, which contributed to the formation of granite in the Isles of Scilly.

Here is a photo to help you with Q2!