The listed coords will bring you close to the Brentford Monument. There is a multi cache here so the coords are slightly off not to superimpose the two listings
Earth Science
The learning element of this EarthCache is to identify Crystal sizes in Granite and what causes the Crystals to vary in size.
Brentford Monument
The peripatetic Brentford Monument was 100 years old on 12 May 2009. Currently sited near Brentford County Court, it is made of Peterhead granite with Potassium K feldspar from Scotland, used in the construction of Brentford Bridge in the 1820s. It was re-used as a monument and erected on Ferry Point in 1909. Since then it has been moved twice.
Watercolour of Brentford Bridge, showing two of the granite cylinders later used for the Monument, from an extra-illustrated copy of Thomas Faulkner’s The History and Antiquities of Brentford, Ealing and Chiswick, 1845.
Granite
Composition
Granite is a hard, coarse-Crystallised igneous rock that forms when magma cools and solidifies underground.
- Granite is made of interlocking crystals of white or pink feldspar, glassy quartz, and shiny mica. It is often used as a building material, and very often as decorative monuments.
Crystal size classification
- Fine-grained: Feldspar crystals are about 1.5 to 3mm in diameter
- Medium-grained: Feldspar crystals are about 65mm in diameter
- Coarse-grained: Feldspar crystals are 125 mm or larger in diameter
The size of the crystals in granite depends on how slowly the magma cooled.
Explanation
- Slow cooling: Slow cooling allows the crystals to grow larger. This typically happens deep underground.
- Fast cooling: Fast cooling results in small crystals.
- Very rapid cooling: Very rapid cooling results in glass.
Classification
- Pegmatite: Granite with especially large crystals (over one centimeter across)
- Aplite: Granite that crystallized in a narrow dike and has a fine texture
Questions
Please message me the answers to the following questions. You can immediately log the cache after you have done so.
Study the Monument:
1. Identify the Feldspar, quartz and Mica. Please describe the colours.
2. Would you say the crystals are course or fine? Please give an average diameter of the Feldspar Crystals.
3. Has the Granite cooled slowly or fast?
4. Would you say the Granite is Pegmatite or Aplite?
Look at the granite blocks on the ground around the monument:
1. Are these blocks made from the same piece of Granite as the Monument? Please give me 2 reasons to justify your answer.
2. Take a picture of your hand holding a piece of paper with your caching name on and the date with one of the granite blocks on the ground behind it.
Thanks for visiting this great monument.