Required: Post a photo of you/your geocaching name/your GPS in front of the St. Mary's sign nearest the lych gate. Do not include the lych gate or church roof in your photo.
To log an EarthCache, you first need to visit the EarthCache site and complete the logging tasks outlined on the cache page. These tasks are designed to teach you about the site's geology and involve making observations and answering questions. After completing the tasks, you'll send your answers to the cache owner, who will then verify your log. You can then log your find on Geocaching.com.
What is Slate?
Slate is a type of rock which was formed when heat and pressure transformed an original shale-type rock composed of clay or volcanic ash. Slate is fine-grained, and usually contains minerals, such as white mica and quartz that are highly resistant to water absorption and weathering. It is also possible to see fossils in slate, which is unusual for this type of rock. Slate is frequently grey in colour, but also occurs in other colours, including shades of grey, from pale to dark, purple, green or cyan (a greenish blue colour). Hematite (streaks a red colour) and chlorite (green colour) contribute to the variations. Slate is made up of parallel foliated plates. This gives it the ability to break smoothly and evenly along its cleavage. The hardness of rocks and minerals is measured using the Mohs scale, which ranges from one to 10 with one being the softest and 10 being the hardest. Slate ranks at 5.5 on the Mohs scale.
Slate as a Roofing Material
Where I'm from in North America, slate roofing dates to the 18th century; during this time, slates were imported, usually from Wales. Today, most European slate comes from Spain. However, there are also slate-producing areas of the UK: Wales (with a museum at Llanberis), Cornwall (famously the village of Delabole), Cumbria (Burlington Slate Quarries, Honister Slate Mine and Skiddaw Slate) and, formerly in the West Highlands of Scotland, around Ballachulish and the Slate Islands in the United Kingdom.
Slate is cost-effective over the potential lifespan of the house or building itself, since it typically lasts for a century or more. In Victorian times, the colours available — dull shades of black, gray, red/purple, green, and blue — were frequently combined to form complex geometric patterns using a variety of butt-end shapes: diamond, square, fish-scale, round, hexagonal, and more. These shapes and colours remain available and in use today, but man-made slate is more common now, although not as durable as the original stone.
Slate - Geological Properties
Slate has two lines of breakability – cleavage and grain – which make it possible to split the stone into thin sheets. In other words, it is the finest grained foliated rock of its particular type. When expertly "cut" by striking parallel to the foliation, with a specialized tool in the quarry, many slates will display a property called fissility, forming smooth flat sheets of stone. In geology, fissility is the ability or tendency of a rock to split along flat planes of weakness (“parting surfaces”). A series of "slate booms" occurred in Europe from the 1870s until the First World War following improvements in railway, road and waterway transportation systems.
Slate is particularly suitable as a roofing material as it has an extremely low water absorption index of less than 0.4%, making the material waterproof. In fact, this natural slate, which requires only minimal processing, has the lowest embodied energy of all roofing materials. Embodied energy is the energy consumed by all of the processes associated with the production of a building, from the mining and processing of natural resources to manufacturing, transport and product delivery. Natural slate is used by building professionals as a result of its beauty and durability. Slate is incredibly durable and can last several hundred years, often with little or no maintenance. Its low water absorption makes it very resistant to frost damage and breakage due to freezing. Natural slate is also fire resistant and energy efficient. In the UK, fixing is typically with double nails onto timber battens (England and Wales) or nailed directly onto timber sarking boards (Scotland and Northern Ireland). Nails were traditionally of copper, although there are modern alloy and stainless steel alternatives. Both these methods, if used properly, provide a long-lasting weathertight roof with a lifespan of around 80–100 years.
Chemical and Physical Weathering
Chemical weathering causes the decomposition, dissolving and loosening of rocks. Chemical reactions destroy the bonds that hold the rocks together. This causes them to break into small pieces. One effect of chemical weathering is hydrolysis (chemical breakdown of a substance when combined with water). Another type of chemical weathering is oxidation. Oxidation is the reaction of a substance with oxygen, and in the case with rocks undergoing oxidation, they become weak and crumble. Carbonation is another form of chemical weathering that causes the formation of carbonic acid which "eats" away at the rock.
Physical or mechanical weathering of rocks is caused by changes unrelated to chemical processes (i.e. breaks down the rock without changing any of its chemical components). One common way is through wedging due to the expansion of ice in rock cracks or wedges. Plants and salt can also cause wedging. Another mechanical weathering process is abrasion by water or wind, or exfoliation due to a lack of physical pressure on the rocks (consequence: rocks split into thinner sheets).
I read and respond to all answers submitted, and will reach out specifically if the answers are grossly incorrect/incomplete. If you are delayed in sending a response, please post a write note with the required photo until you are able to submit the answers. Smileys claimed without sending relevant answers to all questions will be deleted.
Required: Post a photo of you/your geocaching name/your GPS in front of the St. Mary's sign nearest the lych gate. Do not include the lych gate or church roof in your photo.
1) While standing at the posted coordinates (the lych gate roof), identify the colour composition of the slate roof. In your response, describe any differences in colour as well as the overall % of each colour that is represented.
2) Look at the lowest sections of the church roof (not the steeple). Describe the colour and appearance of the slate that you see here. Compare your observations with the lych roof, and explain why/not you think that the slate came from the same quarry.
3) Look closely at the tiles on the lych gate roof (only) and describe the properties of the rock regarding the texture. a) What examples of fissility, if any, can you see? b) Explain why the tiles are either homogenous or heterogenous in mineral and crystal composition.
4) Look at the condition of the tiles. Identify and explain (with examples) the evidence of physical and/or chemical weathering on the lych gate tiles.
5) Post a photo of you/your geocaching name/your GPS in front of the St. Mary's sign nearest the lych gate. Do not include the lych gate or church roof in your photo.
Please no spoilers in photos or logs.
If you are caching in a group, you may all submit the same answers, and EACH PERSON must submit the required photo demonstrating they were on site (see Q5).
Thanks for visiting!
Updated Mar 2024 to better reflect the actual difficulty of this EC.