This is an accessible EarthCache that will take you to the War Memorial in Colchester.
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/or 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.
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.
The steps and plinth of the war memorial are made of granite and limestone
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).
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:
Chemical weathering is caused by rainwater reacting with the mineral grains in rocks to form new minerals (clays) and soluble salts. These reactions occur often when the water is slightly acidic. These chemical processes need water, and occur more rapidly at higher temperature, so warm, damp climates are best. There are different types of chemical weathering, the most important are:
Solution (Carbonation) - removal of rock in solution by acidic rainwater. In particular, limestone is weathered by rainwater containing dissolved CO2.
Hydrolysis - the breakdown of rock by acidic water to produce clay and soluble salts.
Oxidation - the breakdown of rock by oxygen and water, often giving rocks a rusty-coloured weathered surface.
Biological weathering is the impact of living organisms on the stone. Plants put down roots through joints or cracks in the rock in order to find moisture. As the plant grows, the roots gradually pull the rock apart. Many animals bore into rocks for protection either by scraping away the grains or secreting acid to dissolve the rock. Even the tiniest bacteria, algae and lichens produce chemicals that help break down the rock on which they live, so they can get the nutrients they need
Physical weathering is caused by the effects of changing temperature on rocks, causing the rock to break apart. The process is sometimes assisted by water. There are two main types of physical weathering:
Freeze-thaw occurs when water continually seeps into cracks, freezes and expands, eventually breaking the rock apart.
Exfoliation occurs as cracks develop parallel to the land surface, a consequence of the reduction in pressure during uplift and erosion.
Questions
1. Describe the colour, texture, composition of the the main body (South side) of the memorial. Describe the contrast between this main body and the two adjacent sides (East and West sides)
2. Observe the 3- stepped base; which rock in the description is this made from? Explain the features that tell you this.
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 :)