The land around Calderdale is one that has shaped the industry and life of those that have lived here. The steep sided valley and open moorlands mean to get many a spot of geological interest involves a leg stretch, sweating and effort, but there is a spot in the town itself which you can approach without much effort, and get up close and intimite with a bit of geology. The idea of this earthcache, is for you to encounter a stone, and then use the information below to work out what type of stone it is.
Now it being an earthcache, they will be questions to answer (please see below), but first a bit of geology, which will help you take your first steps as a petrologist. Please do not include your answers in your logs.
Types of Rocks
There are three types, Igneous, Metamorphic and Sedimentary.
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.
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.
Common Rock Types
Sandstone can be grey, red or yellow in colour. You will be able to identify lines which 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.
Basalt is a dark igneous rock, and is made up of fine particles, because it cooled rapidly after it came out of a volcano. It is unsuitable for buildings since it is very hard and difficult to fashion into blocks for building.
Marble This is limestone that has been subjected to intense pressure underground due to tectonic movement. 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.
Granite This is an igneous rock and will look a little like concrete, being made up of noticeably different crystals of different coloured minerals. You won’t be able to identify fossils because it forms from the cooling down of molten material. This is very good building material since it has no linear weaknesses.
Limestone A common building material especially in ancient times due to the decorative look of the rock. This is a white rock which suffers from chemical weathering, as a result of acid rain.
Questions
1. Walk round the rock, with your hand on the surface as you go round, what does it feel like?
2. Look closely at the rock, what colour is it, what is it formed of?
3. How tall is the rock?
4. What type of rock is it?