Spheroidal weathering is a form of chemical weathering that affects jointed bedrock and results in the formation of concentric or spherical layers of highly decayed rock within weathered bedrock that is known as saprolite. When saprolite is exposed by physical erosion, these concentric layers peel (spall) off as concentric shells much like the layers of a peeled onion. Within saprolite, spheroidal weathering often creates rounded boulders, known as corestones or woolsack, of relatively unweathered rock. Spheroidal weathering is also called onion skin weathering, concentric weathering, spherical weathering, or woolsack weathering. [SOURCE]
Rocks star out as cube-shaped forms but the the alteration by weathering of the bedrock will be greatest along the corners of each block, followed by the edges, and finally the faces of the cube. The differences in weathering rates between the corners, edges, and faces of a bedrock block will result in the formation of spheroidal layers of altered rock.
At this cache location, observe the floor and you should easily recognise several features that have resulted from spheroidal weathering. These basalts are common throughout the Lisbon district as a result of the Lisbon Volcanic Complex eruptions (see EC GCPZC9 for further evidence of the LVC).
To validate your find in this EC, please answer the following questions:
1- If you were to reconstruct the "balls" (remember they now have flat tops due to erosion), how big would they be? Tennis ball size? soccer ball size? small car size? or larger than that?
2- Look closely at the layers. What is the average thickness of these and are they uniform in thickness?
3- The rocks are heavily weathered. Observe the rock closely. Based only on the different colours of the minerals visible to the naked eye, how many different minerals can you identify?
EN - In order to finish the validation of your find, you have to send me the answers to the questions above either though the geocaching message center service or my profile. Thanks
A disjunção esferoidal é uma forma de erosão química que afeta a rocha fracturada e resulta na formação de camadas concêntricas ou esféricas de rocha altamente deteriorada na rocha erodida, conhecida como saprolito. Quando o saprolito é exposto pela erosão física, essas camadas concêntricas desprendem-se em lascas concêntricas, como as camadas de uma cebola descascada. Dentro do saprolito, o desgaste esferoidal geralmente cria rochas arredondadas, conhecidas como casca de cebola. [traduzido da FONTE]
Originalmente as rochas aparentam formas em forma de cubo, mas a alteração pelo desgaste da rocha é maior nos cantos de cada bloco, seguidos pelas bordas e, finalmente, pelas faces do cubo. Por esta razão, as diferenças nas taxas de erosão entre os cantos, arestas e faces de um bloco de rocha irão resultar na formação de camadas esferoidais de rocha alterada.
Na localidade desta EC, irão mais uma vez ver basaltos resultantes do Complexo Vulcânico de Lisboa. Obervem o chão com atenção especilamente no meio onde a água corre.
Para validar o FOUND, respondam à seguintes perguntas:
1- Se reconstruísses as "bolas" (lembra-te de que agora elas têm faces planas devido à erosão), qual seria o tamanho delas? Tamanho da bola de tênis? tamanho da bola de futebol? tamanho de carro pequeno? ou maior que isso?
2- Olha atentamente para as camadas. Qual é a espessura média destas? A sua espessura é homogénea?
3- Este afloramento encontra-se muito alterado. Observa atentamente a rocha alterada. Com base nas cores dos minerais visíveis a olho nú, quantos minerais diferentes consegues identificar?
PT - Para terminar a validação do teu "find", tens de me enviar as respostas às perguntas via o serviço de mensagens do geocaching or pelo meu perfil. Obrigado.
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 The most exciting way to learn about the Earth and its processes is to get into the outdoors and experience it first-hand. Visiting an Earthcache is a great outdoor activity the whole family can enjoy.
An Earthcache is a special place that people can visit to learn about a unique geoscience feature or aspect of our Earth. Earthcaches include a set of educational notes and the details about where to find the location (latitude and longitude). Visitors to Earthcaches can see how our planet has been shaped by geological processes, how we manage the resources and how scientists gather evidence to learn about the Earth. To find out more click HERE.
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