This earthcache will take you to the old General Post Office at the south side of George Square.
The purpose of this earthcache will help you learn about Xenoliths and how they are formed.
Igneous rocks form when molten rock originating from deep within the earth’s crust cools (either below the surface as an intrusion e.g. granite, or above the surface as an extrusion e.g. basalt lava). The resulting igneous rock is composed of interlocking crystals, the size of which depends on the time taken for the molten rock to cool. If the molten rock cooled rapidly, the crystals are small if it cooled slowly, the crystals will be large. A common building stone of the latter type is granite – due to the large crystal size in granite it is a very aesthetically pleasing rock, and as such is found in many forms, cladding buildings around Glasgow and also being used for ornamental pillars and balustrades.
A number of blonde sandstones: Dunmore (Stirlingshire), Giffnock (Glasgow), and Hermand (West Lothian) have been used for this building. The pillars are composed of Ross of Mull granite, with pink crystals of the mineral feldspar and large black xenoliths. A xenolith is an inclusion in the magma which formed the granite and quite often it is part of the existing country rock into which the magma was forced.
Look at the pillar to the right of the doorway and then the xenolith as indicated by the arrow in the photograph.
There are several examples of xenoliths in this pillar. Look at the pillar and answer the following questions:
Q1. You should be able to see a large xenolith at the bottom of the pillar. What distinguishes it from the granite surrounding it?
Q2. Describe the size and shape of the xenolith.
Q3. How do you think the xenoliths got there?
Q4. Please provide a photo of yourself or a personal item near GZ (without giving away the answers).
Answers to questions 1-3 should be sent by the message centre or email. Please DO NOT include the answers in your log.
Please send your answers BEFORE logging the cache. You do not need to wait for a reply, but if there is a problem, we will let you know.
ANY LOGS ENTERED WITHOUT ANSWERS BEING SENT WITHIN TWO WEEKS WILL BE DELETED.
