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, which then forms crystals which make up the rock. 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 peppering the lighter colour minerals.
A phenocryst is a crystal in igneous rock, that is larger than the surrounding crystals of the rock that it forms part of.
Quartz is the second most abundant mineral in the continental crust. It is a defining constituent of granite and other felsic igneous rocks, and is very common in sedimentary rocks such as sandstone and shale. While the majority of quartz crystallizes from molten magma, much quartz also chemically precipitates from hot hydrothermal veins as gangue, sometimes with ore minerals like gold, silver and copper. It is formed from silicone and oxygen, with the chemical formula SiO2. It can come in a variety of colours, but in the case of this type of granite it tends to be clear or milky coloured.
Feldspar is one of the most common group of minerals in the earth's crust, forming about 60% of terrestrial rocks. Most deposits offer sodium feldspar as well as potassium feldspar and mixed feldspars. It can be white, pale grey or pink.
Biotite Mica is a common rock forming mineral, and is present in most igneous rocks. Its is typically black to brown in colour. The darker colour increases due to increased iron content.
Amphibole forms prism or needlelike crystals, and can be green, black, colourless, white, yellow, blue, or brown.
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1) How big is the largest phenocryst (crystal) on the memorial?
2) What colour are the phenocrysts in the memorial?
3) Which mineral do you think is the most frequent in this stone?