URBAN EARTH - Rock Detective EarthCache

Introduction

One part of playing amateur geologist is trying to identify the type of rock we are looking at. If we're lucky, sometimes there's stuff trapped or included in the rock that helps to make identification easier. This EarthCache offers an opportunity to identify a rock type by looking at those features.

At the published coordinates you will find a building with very nice, ornate, pale coloured dimension stone cladding and it's that cladding you need to study.

You won't need a magnifying glass or anything like that but anyone who relies on spectacles for reading will likely enjoy the experience more by wearing them.

Logging Tasks

IN ORDER TO COMPLETE THESE LOGGING TASKS PLEASE SEND US YOUR ANSWERS USING THE Message this owner LINK AT THE TOP OF THIS PAGE OR USING THE MESSAGE CENTRE OR EMAIL VIA OUR GEOCACHING PROFILE BEFORE SUBMITTING YOUR LOG. PLEASE DO NOT INCLUDE ANSWERS OR SPOILERS IN YOUR ONLINE LOG. YOU CAN GO AHEAD AND LOG YOUR FIND AS SOON AS YOU HAVE SENT YOUR ANSWERS IN ACCORDANCE WITH GROUNDSPEAK GUIDELINES. LOGS WITHOUT ADEQUATE LOGGING TASK EVIDENCE MAY SUBSEQUENTLY BE DELETED.

Based on your study of the stone cladding and using the information on the cache page please tell me:

1. Is this stone sedimentary, metamorphic or igneous?
   
   
2. What leads you to your conclusion?
   
   
3. How do you know this rock IS NOT either of the other two types?
   
   
4. Optional task: feel free to add any photographs of your visit that do not show the specific features from the logging tasks - no spoilers please. In the interests of allowing everyone to experience the EarthCache fully for themselves obvious spoiler photographs will be deleted.
   
   

Background

All rocks are made of minerals and if you're lucky enough to be able to identify different minerals on sight that will certainly contribute towards your ability to identify what sorts of rocks you are looking at.

Sometimes the visible structural characteristics of the rock can assist with identification - a matrix of sand-sized grains typically points to sandstone which is a sedimentary rock for example, ingneous rocks such as granite usually have a clearly visible crystalline structure and metamorphic rocks often display foliation in the form of obvious bands of light and dark material running through the rock.

Associated Rock Type Features

For the purposes of this EarthCache we'll limit ourselves to three types of features which may be observed and assist in rock identification.

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  Fossils - any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals, hair and petrified wood.
  
  Fossils are found almost exclusively in sedimentary rocks because the sediments are laid down in such a way that they preserve the shape of the living organism's remains during lithification (the process of becoming rock).
  
  The temperatures and / or pressures typically present during the formation of metamorphic or igneous rocks tend to destroy fossil remains.
  
  
  
  
• 
  Porphyroclasts - metamorphic rocks start off as one rock type which, when subjected to extreme heat and / or pressure, metamorphoses into a different type of rock.
  
  Sometimes, even though the rock is subjected to enough heat and / or pressure to destroy any fossil fragments present before metamorphosis, some parts of that original rock are stronger than other parts and resist being re-crystalised, instead remaining as fragments of that original rock, surrounded by a finer groundmass of crystals of the new rock. Thus porphyroclasts are always older than the surrounding material.
  
  
  
  
  
• 
  Xenoliths - xeno-lith literally foreign stone from the greek xenos and lithos.
  
  A xenolith is a piece of rock trapped in another type of rock. Most of the time, a xenolith is a rock embedded in magma while the magma was cooling.
  
  Magma is the molten rock beneath the Earth's crust that emerges as lava during a volcanic eruption. The rock that forms from cooled magma is called igneous rock. During the eruption the magma forces its way up through the layers of crust to the surface, picking up fragments of foreign rock as it rises which remain as xenoliths when the magma cools and solidifies.
  

If you've carefully read and digested the information from this cache page your tasks at the cache location should prove relatively straight forward, although you may wish to take a printed copy of the page with you so that you can check your answers while there .

Please submit your logging task responses before posting your log.