Earthcaches are there for us to learn and see, but many of them are off the beaten track, where not all can get to, this is an attempt to try and meet the need of others who are not as able as others.
Bury, is one of those Lancashire towns that many just associate with black pudding and the market, but spend you time looking and there is geology to be had. This earthcache takes you to Kay Gardens in Bury, which is an easy walk / wheelchair push / mobile ride from the town centre.
The gardens commemorate John Kay, born in Bury in 1704 and inventor of the flying shuttle. You need to go to the Memorial to John Kay, inventor of the Flying Shuttle. It is an ornate, Italianate domed octagon, 34 ft high, composed of horizontally rusticated based sandstone, re-used from old market, and 8 red granite ionic columns broken forward under entablature frames panels depicting looms, except on side bearing medallion of Kay. The dome is of Portland stone encircled by balustrade, surmounted by bronze figure of Fame and surrounded by smaller figures of Agriculture, Engineering, Mining and Weaving.
I have brought you here to look at the red granite columns. You will need to go up the steps to them, or look from the pavement level.
What is Granite?
Granite is a common type of igneous rock. Igneous rock is one of the three main rock types , the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or lava. Igneous rock may form with or without crystallisation either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. Granite is granular can be described as phaneritic and felsic in texture. Granites can be predominantly white, pink, or gray in color, depending on their mineralogy. By definition, granite is an igneous rock with at least 20% quartz and up to 65% alkali feldspar by volume. Phaneritic is a term usually used to refer to igneous rock grain size. It means that the size of matrix grains in the rock is large enough to be distinguished with the unaided eye as opposed to aphanitic (which are too small to be seen with the naked eye). This texture forms by the slow cooling of magma deep underground in the plutonic environment.
Granitic rocks mainly consist of feldspar, quartz, mica and amphibole minerals, which form an interlocking, somewhat euuigranular matrix of feldspar and quartz with scattered darker biotite mica and amphibole (often hornblende) peppering the lighter color minerals. Occasionally some individual crystals ( phenocrysts) are larger than others, in which case the texture is known as porphyritic. A granitic rock with a porphyritic texture is known as a granite porphyry. Granitoid is a general, descriptive field term for lighter-colored, coarse-grained igneous rocks.
Phenocryst
This is a relatively large and usually conspicuous crystal distinctly larger than the grains of the rock of an igneous rock. Such rocks that have a distinct difference in the size of the crystals are called porphyries, and the adjective porphyritic is used to describe them. Phenocrysts often have euhedral forms, either due to early growth within a magma, or by post-emplacement recrystallization. Euhedral crystals are those that are well-formed with sharp, easily recognised faces. The opposite is anhedral: A rock with an anhedral texture is composed of mineral grains that have no well formed crystal faces or cross-section shape in thin section. Anhedral crystal growth occurs in a competitive environment with no free space for the formation of crystal faces. An intermediate texture with some crystal face formation is termed subhedral.
Normally, crystals do not form smooth faces or sharp crystal outlines. Many crystals grow from cooling liquid magma. As magma cools, the crystals grow and eventually touch each other, preventing crystal faces from forming properly or at all.
Normally the term phenocryst is not used unless the crystals are directly observable, which is sometimes stated as greater than .5 millimeter in diameter. Phenocrysts below this level, but still larger than the groundmass crystals, are termed microphenocrysts. Very large phenocrysts are termed megaphenocrysts. Some rocks contain both microphenocrysts and megaphenocrysts.
Classification by phenocryst. Rocks can be classified according to the nature, size and abundance of phenocrysts, and the presence or absence of phenocrysts is often noted when a rock name is determined. Aphric is a term used to describe rocks that have no phenocrysts, or more commonly where the phenocrysts consist of less than 1% phenocrysts (by volume); while the adjective phyric is sometimes used instead of the term porphyritic to indicate the presence of phenocrysts.
This being an earthcache, in order to log it, I ask that you answer some 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.
(1) What colours in the granite are there?
(2) Please touch the granite. How does it compare to the other parts of the memorial, ie is it rough / smooth?
(3) Are the crystals Euhedral, anhedral or subhedral?
(4) Can you see any phenocrysts?