The Woven Globe of Darwen 

Many may just assume that earthcaches are in out of the way places and may get put off by that aspect. Though they can be found in urban places, you just need to look, or as the town motto says "ABSQUE LABORE NIHIL" "NOTHING WITHOUT LABOUR". The Woven Globe by artist Sebastian Boysten was commissioned to commemorate the millennium and sits at the top end of Church Street. The globe is twinned with a similar piece in Darwen Town Centre and celebrates the commercial and industrial past of Blackburn and Darwen.

In order to get the best out of this cache you need to get up close to the globe and look at its innarts, no arm chair logging for this one. 

I have brought you here to look at the granite guts of the sculpture. 

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 toaphanitic  (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.  Is it rough / smooth?

(3) Are the crystals Euhedral, anhedral or subhedral?

(4) Can you see any phenocrysts?