This EarthCache is 2/3 on a series of EC's on the subject of the textures of igneous rocks.
What is texture in a rock?
The texture of a rock is the size, shape, and arrangement of the grains (for sedimentary rocks) or crystals (for igneous and metamorphic rocks).
Porphyritic texture
This texture describes a rock that has well-formed crystals visible to the naked eye, called phenocrysts, set in a very fine grained or glassy matrix, called the groundmass. A porphyritic texture is developed when magma that has been slowly cooling and crystallising within the Earth's crust is suddenly erupted at the surface, causing the remaining uncrystallised magma to cool rapidly.
Validating your FIND:
- Can you see different colours in the rock? How many different ones can you you see and based on this what can you tell from this about it's composition?
- The green phenocrysts (large crystals in the fine-grained rock) are olivine. Describe their shape, variation in size and their fracturing pattern?
WARNING: Watch out for the tide! Do not attempt this cache on stormy days and during high tide.
Esta EarthCache é 2/3 na temática das texturas de rochas ígneas.
A que se refere a textura numa rocha?
A textura de uma rocha é o tamanho, forma e disposição dos grãos (para as rochas sedimentares) ou cristais (para as rochas ígneas e metamórficas).
Textura porfirítica
Esta textura descreve uma rocha que possui cristais bem formados visíveis a olho nu, denominados fenocristais, inseridos em uma matriz de grão fino ou vítreo. Uma textura porfirítica é desenvolvida quando o magma que arrefece lentamente e cristaliza dentro da crosta terrestre e é depois repentinamente irrompido na superfície, fazendo com que o magma não cristalizado restante arrefeça muito rapidamente.
Para validares a tua visita:
- Quantas cores diferentes podes distinguir nestas rochas? Baseado nestas, o que podes dizer sobre a sua composição?
- Os fenocristais (cristais grandes) são olivina. Descreve a olivina no que se refere a sua forma, a sua variação de tamanho e a sua fracturação
AVISO: Cuidado com a maré! Não tentes fazer esta cache em dias de maré alta ou tempestade.
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.