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Welcome to the forty continuation AGT series (Alke Geoearthcache tour). This time we visit the Vatican, where there is a large granite obelisk.
A large pink granite obelisk can be admired in the center of the square. It was hewn from a single block and stands 25.31 m. high on a base 8.25 m. wide. The obelisk which comes from Heliopolis in Egypt.
Granite forms when bits of quartz and feldspar are shot out of volcanoes, so it's one kind of igneous rock. The word "granite" comes from the Latin word "granum", a grain, because granite is made of lots of smaller bits of quartz and feldspar stuck together (think of our word "granary", a place where you store grain). Granite comes in different colors, usually pink (as here) to gray or sometimes black.
Granite's a very hard stone. It's hard because it formed as hot liquid stone, and so the molecules inside it are all jumbled up any which way, instead of lying in layers as in sedimentary rocks like limestone or slate.
Because granite is so hard, people sometimes use it for building stone or statues if you want them to last a long time. But granite is so hard that it's also hard to cut into blocks or statues. In ancient Egypt, sculptors used granite to carve statues of pharaohs or obelisks.
Granite is often distorted defects which are manifested in different colors and often disrupt the cohesion of the rock. This monolith is interesting that almost no defects does not. It is due to the fact that when volcanic activity management, when the rock was formed, the process was not interrupted by rocks or other chemical processes. Single defects rock located at a height of 18 m and is caused by the different composition of the rocks in place. Nothing less, thus ones kind of pink granite without caries is unique.
The speed at which granite cools directly relates to the size of the crystals. The slower the cooling is, the more time the minerals have to form large crystal. In other words: if the obelisk has small crystals, then you know it has cooled quickly.
The appearance and color of granite determined mainly feldspar which contains. Color alkali feldspar is usually yellowish and yellowish decorative but can be pink to red flesh color. Color other feldspar in granite - plagioclase is mostly white, other colors are rare. Plagioclase granite give a glassy luster. Generally, the feldspars, if they are unweathered predominates white, bluish-white and ping color. In the case of weathering begins to prevail yellowish and brownish color.
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