This is an accessible EarthCache that will take you to the War Memorial in the city of Cambridge.
Here you will undertake a geology lesson as you visit this memorial.
As this is an EarthCache you need to send me your answers via email or the message centre.
Types of Rocks
There are three types, Igneous, Metamorphic and Sedimentary.
Sedimentary rocks are types of rock that are formed by the deposition and subsequent cementation of that material at the surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles to settle in place. The particles that form a sedimentary rock by accumulating are called sediment. Examples of this rock are sandstone and limestone.
Igneous rock is formed through the cooling and solidification of magma or lava. An example of this is granite.
Metamorphic rocks arise from the transformation of existing rock types, in a process called metamorphism, which means "change in form".The original rock is subjected to heat and pressure, causing profound physical and/or chemical change. An example of this is marble.
A few common rocks and identifying features
Marble is a metamorphic rock, It is formed from limestone that has been subjected to intense pressure underground due to tectonic movement or through being subject to extreme heat. This rock is generally white with different coloured veins running through it. It is a very tough rock and would feel very smooth even after years of exposure to the elements.
Basalt is a dark igneous rock, and is made up of fine crystals, because it cooled rapidly after it came out of a volcano. Basalt does not contain any bedding planes. It is unsuitable for buildings since it is very hard and difficult to fashion into blocks for building, it can however be used more crudely for building simple walls.
Slate is a metamorphic rock. It is a fine grained rock of sedimentary origin. It is waterproof and extremely durable, Slate occurs in a variety of colours from pale to dark. Due to its durability it has often been used for tombstones and memorial tablets.
Granite This is an igneous rock made up of noticeably different crystals of different coloured minerals. Granite may contain crystal structures of different sizes.
In some examples of granite, you may find phenocrysts. A phenocryst is an early forming, relatively large and usually conspicuous crystal distinctly larger than the grains of the rock groundmass (the surrounding material).
Sandstone is a sedimentary rock, it can be grey, red or yellow in colour. You will be able to identify the bedding planes which are lines that run all the way through the rock, where different seasons or catastrophic events have altered the composition of the deposits for a short time. The rock will be quite durable but feel rough to the touch and small grains will come off when you rub it vigorously.
Limestone is a sedimentary rock. A common building material especially in ancient times due to the decorative look of the rock and its propensity to being easily carved. This is often a light coloured rock, but other limestones may be variously coloured including darker colours. which suffers from chemical weathering, as a result of acid rain. It may contain bedding planes and many variety of fossils including corals, shells and marine life.
Weathering
The weathering of rocks is quite simply the breaking down of the stone at the Earth's surface, by action of rainwater, extremes of temperature, or biological activity. It doesn't involve the removal of rock material. There are three main types of weathering:
Physical weathering is caused by physical processes such as changes in temperature, freezing and thawing, and the effects of wind, rain and waves. An example of physical weathering is freeze-thaw weathering, where water expands slightly when it freezes to form ice. The formation of ice can break rocks, as if water gets into a crack into the rock, it freezes into ice, expanding the crack and making it bigger. This process then repeats itself with the crack in the rock getting bigger every time.
Chemical weathering occurs when the minerals within the rocks are chemically altered. In the process of carbonation, rainwater and carbon dioxide in the atmosphere combine to form carbonic acid. This means all rainwater is slightly acidic. This carbonic acid dissolves minerals within the rock, weakening the structure and resulting in damage and wear. On statues or monuments this can also result in the appearance of staining on the surface.
Biological weathering is where rock is weakened and disintegrates from the impact of plants, animals and microbes. These can release acid forming chemicals that contribute to the rock breaking down (weathering). Examples of this would include moss or lichen growing through the rock. Growing plant roots can exert stress or pressure on rock, potentially causing it to crack.
Questions
1. Take a walk around the memorial. Look carefully at the colour, texture and general appearance of the main body of the memorial, and describe what you see.
2. From the EarthCache description and your answer to Q1, what rock do you think the plinth is made from, and why?
3. Examine the main memorial block again, but this time looking for signs of weathering. Has the memorial been stained? Has it been affected by physical/chemical/biological weathering or a combination?
4. Please add a photo of you or your GPS at the memorial though not giving any answers away :)