As you leave Glasgow Queen Street station, and cross West George Street, you notice a building covered in large granitic panels. We are here to look at the crystals in these panels. More specifically, we are here to look at phenocrysts.
A phenocryst is a crystal in igneous rock, that is larger than the grains of the rock that it forms part of.
Rapid cooling of igneous rocks, can lead to small crystals, whilst larger crystal size occurs when there is slower cooling.
Phenocrysts can have different forms :
They can be euhedral, these crystals are well defined, sharp and easily recognisable edges.
They can be anhedral, which do not have well defined edges
This is meant to be an easy enjoyable EarthCache, that children can enjoy and learn from, so there is not a lot in the description , to blind you with science, it is mean to be about doing, learning and exploring, so lets do that, by completing some tasks :
(1) Please look at the phenocrysts , what colour are they?
(2) Are these phenocrysts euhedral or anhedral?
(3) Please measure the biggest phenocyrst you can find, and tell me its dimensions.