This EarthCache takes you to the Prescott Fountain in Halifax. This is not meant to be a difficult EarthCache to do, but it is one that you will need your eyes, and measuring skills to do.
THE “PRESCOTT FOUNTAIN.”
THIS FOUNTAIN WAS PRESENTED BY
MRS LEIGH OF SUMMERVILLE
TO THE CORPORATION OF HALIFAX
IN THE MAYORALTY OF ALFRED RAMSDEN ESQ.
ON THE 12TH DAY OF SEPTEMBER 1884
This fountain has four taps, two large troughs for horses, and four smaller troughs for dogs. It also had a lamp on top. It was originally in Fountain Street. In 1898, it was moved to King Cross, Calderdale to make way for the construction of the tramway until it was moved for road improvements. On 22nd August 1932, it was moved to Spring Edge where it still stands today.
The stone that makes up the fountain is made up of granite, now there are already some other EarthCaches in Halifax which describe this stone, so we will not diverge too much into the subjectology. What we are here to look at is crystal shape, or to be more specific, phenocryst shape. Again there are some EarthCaches which describe phenocrysts, but lets look in a bit closer detail. First some background, looking at the microstructures and macrostructures can help provide information on how quickly it cooled, and what it is formed of. Granite is formed of crystals, of which some can be described as phenocrysts. Igneous rock forms by crystallisation either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. Intrusive rock forms within the crust from the crystallization of magma. As the magma pushes up from deep, it eventually slowly cools into a solid, and forms rock. An intrusive rock is any form of igneous rock that forms within the crust of the planet. Large areas of magma that solidify underground before they reach the surface are known as plutons .Granitic rocks mainly consist of feldspar, quartz, mica and amphibole minerals, which form an interlocking matrix of feldspar and quartz with scattered darker biotite mica and amphibole (often hornblende) peppering the lighter colour minerals.
A phenocryst is a crystal in igneous rock, which is larger than the crystals of the rock that it forms part of.
Phenocrysts can have different forms:
Euhedral - these crystals are well defined, sharp and easily recognisable edges.
Anhedral – these crystals do not have well defined edges.
So basically phenocryts are crystals, now these can be classified in terms of shape.
This being an EarthCache, in order to log it, I ask that you answer the below questions . Please send them to me, and do not include them in your log. You can send them to me by using the message facility or email, both of which can be found by looking at my profile. Alternatively, they can also be given face to face should we meet.
(1) Please look at the base of the water fountain, here you can see a number of phenocrysts. Please describe their shape, and colour.
(2) Using the above EarthCache lesson, please tell me whether you think this granitic rock cooled quickly or slowly, what is the rationale for your answer?
(3) Are the phenocrysts, anhedral or euhedral?