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The Great Zimbabwe Ruins are built from Granite.This cache is presented to help you, as a visitor to this spectacular site, understand the medium with which it was built. Enjoy your visit.
Granite is a light-colored igneous rock with grains large enough to be visible with the unaided eye. It forms from the slow crystallization of magma below Earth's surface. Granite is composed mainly of quartz and feldspar with minor amounts of mica, amphiboles, and other minerals. This mineral composition usually gives granite a red, pink, gray, or white colour with dark mineral grains visible throughout the strong rock.
What Determines Granite Colours? Granite is a conglomerate of minerals and rocks, primarily quartz, potassium feldspar, mica, amphiboles, and trace other minerals. Granite typically contains 20-60% quartz, 10-65% feldspar, and 5-15% micas (biotite or muscovite). The minerals that make up granite give it the unique colors we see in different types of granite. The relative proportion of different coloured minerals in a granite is largely due to the original source of molten rock that cooled to form the granite. If the molten rock was abundant in potassium feldspar, the granite is more likely to take on a salmon pink colour. On the other hand, if the molten rock is abundant in quartz and minerals that make up amphibole, you will likely get a black and white speckled granite commonly seen on countertops.
Quartz - typically milky white colour
Feldspar - typically off-white colour
Potassium Feldspar - typically salmon pink colour
Biotite - typically black or dark brown colour
Muscovite - typically metallic gold or yellow colour
Amphibole - typically black or dark green colour
The combination of the minerals above make up most of the colours we typically see in a granite. Granite is nearly always massive and very hard. The average density of granite is between 2.65 and 2.75 g/cm, its compressive strength usually lies above 200 MPa, and its viscosity near STP is 3–6 • 10 Pa•s. The melting temperature of dry granite at ambient pressure is 1215–1260 °C it is strongly reduced in the presence of water, down to 650 °C at a few kBar pressure. Granite has poor primary permeability, but strong secondary permeability. Granite is classified as igneous, arising from magma many miles below the surface. Granite formation begins when two tectonic plates collide. One plate will be pushed under the other creating a subduction zone. Rocks in the down-going plate are super-heated under extreme pressure, up to 1,600 degrees C, melting into magma which then rises upwards because it is hot and less dense than the surrounding material. About 10% of the magma will be pushed to the surface, erupting as volcanoes where rapidly cooling lava creates a variety of fine-grained rocks from basalt to obsidian. However, 90% of the magma will remain deep below the surface cooling slowly over a long period of time forming irregular masses of granite, which can be extremely variable in size, ranging from less than a few square miles to larger masses (batholiths) that are often hundreds or thousands of square miles in area.
Beneath every mountain range formed over a subduction zone lies a huge bed of granite. Over eons, uplift and erosion removes miles of bedrock to expose the granite domes and outcrops. Many people recognize granite because it is the most common igneous rock found at Earth's surface and because granite is used to make many objects that we encounter in daily life. These include counter tops, floor tiles, paving stone, curbing, stair treads, building veneer, and cemetery monuments. Granite is the rock most often quarried as a "dimension stone" (a natural rock material that has been cut into blocks or slabs of specific length, width, and thickness). Granite is hard enough to resist abrasion, strong enough to bear significant weight, inert enough to resist weathering, and it accepts a brilliant polish. These characteristics make it a very desirable and useful dimension stone. Granite has been used for thousands of years in both interior and exterior applications. Rough-cut and polished granite is used in buildings, bridges, paving, monuments, and many other exterior projects. Indoors, polished granite slabs and tiles are used in countertops, tile floors, stair treads, and many other practical and decorative features.
Granite is also used as a crushed stone or aggregate. In this form it is used as a base material at construction sites, as an aggregate in road construction, railroad ballast, foundations, and anywhere that a crushed stone is useful as fill.
The most spectacular use of granite is the Ruins at the Great Zimbabwe. Each block has been cut from a granite outcrop and used to build the most spectacular Acropolis and Temple. The climb up the granite outcrop will take you to the ruins at the tops of the hill known as the Acropolis. Access to the ruins will take you through various tunnels/arches. Note the structural manner in which these arches/tunnels have been constructed and the types and shapes of rocks that have been used. As you climb, study the outcrop and try and understand the geology of this stone and how it has been used and mined by our forefathers in years gone by. There are two routes to climb this granite outcrop and they are known as the Ancient Path and the Modern Path.
Please take note of the details of the sign as you will need to know this to answer the questions below. It will also give you the gradient of the climb.
In order to claim this earth cache as a find you need to answer the following questions;
1. What colour would you describe the granite used in the construction of the ruins and what do you think are the prominent minerals in this granite that give it it's general colour. ?
2. What is another name for crushed granite when used in a building context.?
3. What distance do you think it is to climb this outcrop of Granite which houses the “Acropolis” ?
Please email your answers to me via the GC.com website - do not post your answers in your log. You need not wait for confirmation before logging, if there is a problem with your answers I will get back to you. Note that Found logs where an email is not received within 48 hours will be deleted.
Additional Hints
(Decrypt)
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