Major Allan Wilson Memorial
-
Difficulty:
-
-
Terrain:
-
Size: 
(other)
Please note Use of geocaching.com services is subject to the terms and conditions
in our disclaimer.
Background photo shows The Shanagani memorial at the Matopos, the last resting place of Allan Wilson's patrol
The Shangani Patrol (or Wilson's Patrol), comprising 34 soldiers in the service of the British South Africa Company, was ambushed and annihilated by more than 3,000 Matabele warriors during the First Matabele war in 1893. Headed by Major Allan Wilson, (born Glen Urquhart in 1856) the patrol was attacked just north of the Shangani River in Matabeleland in Rhodesia (today Zimbabwe). Its dramatic last stand, sometimes called "Wilson's Last Stand", achieved a prominent place in the British public imagination and, subsequently, in Rhodesian history, mirroring events such as the Battle of Shiroyama in Japan, the Alamo massacre in Texas and the ancient Greeks' last stand at Thermopylae.
Rocks can be divided into three main groups, sedimentary, igneous and metamorphic. The grey and the red stone of this memorial are both granite, (Igneous rock) ~ the type of granite a particular specimen is, depends upon the percentages of minerals that make up the rock, especially quartz (Greyish colour), K-feldspar (Reddish colour), Na-feldspar (White) and Biotite (Black) and sometimes black amphibole hornblende.
Granite is one of the most commonly known types of rocks, used in everything from buildings to sculptures. It has been used for thousands of years and is regarded as a symbol of status, strength, and durability. Granite is a common intrusive plutonic igneous rock. Intrusive means that it has moved into other rocks by force coming up from the mantle. Plutonic means that it is magma that does not reach the surface of the earth and so cools very slowly underground. Igneous (derived from the Latin word ignis meaning fire) 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. Because it cools slowly crystals have time to form. And the slower it cools the bigger the crystals, its name comes from the Latin word granum which means “a grain” for the coarse grain crystalline structure of the rock. Individual crystals are visible to the naked eye in all types of granite. It is made up of quartz, mica, and feldspar. Granite must contain at least 20% quartz within a rock to make it granite. Quartz is one of the last minerals to form in granite; it acts as a bond between other minerals. Although quartz is colourless, it often appears grey because it reflects the colours of dark and light minerals around it.
You will notice on the grey blocks on the right hand side (2 sides round from the front plaque) and also in the steps, some larger dark marks, different to the rest of the grey in the blocks. These marks are called xenoliths, they are part of the original rock which did not melt when the rock was formed.
Below the surface of the earth lies molten rock magma. Floating on this sea of magma, are plates of solid rock. They are the tectonic plates which are in constant movement. Where the plates meet, one plate will slide on top of another plate forcing it down into the sea of magma. The downward pressure causes some of the molten magma to swell up in bubbles and melt some of the rock above. The molten rock under great pressure from the solid plate above cools slowly to form large crystals. Not all the original rock melts and fragments of it remain in the rock which is how these dark patches (xenoliths) are formed.
Granite comes in a wide variety of colours including reds, browns, and many shades of grey from almost black to nearly all white. Granite is a mix of minerals and rocks, primarily quartz, potassium feldspar, mica, amphiboles, and other trace 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 colours we see in different types of granite.
The relative proportion of different coloured minerals in 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 black and white speckled granite.
• 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 granite.
Red granite is a variation of pink potassium feldspar abundant granite, where the k-feldspar takes on a redder than pinker colour. Also, you can get red colouring from iron oxide in hematite grains or inclusion within feldspar, essentially the same process that makes rusted metal red coloured.
To claim this earthcache, please send the answers to the questions below to us by email /message centre, do not post in your online log. Your log may be deleted if these criteria are not met. It is helpful if you send your answers and log at the same time. Educational guidelines for Earthcaches are set by Geocaching.com and GeoSociety.org (Earthcache) and have to be adhered to. While not compulsory, it is always nice to see photos of your visit
1) Looking at the grey granite, you see both polished and unpolished granite ~ of which do you find the crystals easier to see and why?
2) Compare the size of the crystals in the pink flat top (housing the metal work) to that of the grey granite bases of the 6 pink pillars. Are they about the same size or do they differ? If they differ, which colour has the larger size, what size are they and why do you think this is?
3) Look at the xenolith in the bottom step at the rear of the memorial.
a) How does it differ in colour to the rest of the step and why do you think this is?
b) Approximately how long and how wide is it?
4) There seems to be more xenoliths in the grey, but there is also some in the pink. Where can you see one in the pink blocks and how would you describe its shape?
5) Although not granite, you sometimes find another rock referred to as ‘Blue Granite’, what is this rock and where is it commonly found? (Google may help)
Additional Hints
(No hints available.)