Rocks can be generally classified into three groups – sedimentary, igneous and metamorphic.
Sedimentary rocks are made up of fragments of other rocks. When rocks are weathered or broken down they form particles called sediments also known as clasts. These clasts may be transported by wind or water and deposited at a new location. Over time the clasts are compacted and cemented together forming a new rock. Rocks formed this way are referred to as clastic sedimentary rocks. They can be identified by the size of the sediment within the natural cement. Note - There are other types of sedimentary rocks however they aren’t relevant for this Earthcache.
Igneous rocks are said to be ‘fire born’. These result from the cooling and crystallisation of molten rock otherwise known as magma. Magma forms deep within the Earth and usually reaches the surface through volcanic vents. Once the magma flows on the surface of the Earth it is referred to as lava. Igneous rocks are made up of interlocking crystals that vary in size depending on how fast the molten material cooled. If cooling is fast then the crystals are very small less than 1mm in size. This would happen when molten material that has flowed out onto the surface of the Earth to cool. Magma that cools within the Earth’s crust take much longer to crystallise and resulting size of the crystals is between 1 – 10 mm.
Metamorphic rocks are the result of other rocks being transformed. This happens when heat and pressure causes changes to the chemistry and physical appearance of the original rock. The original rock, known as the protolith or parent rock, may be sedimentary, igneous or another type of metamorphic rock. For example limestone can be transformed into marble and granite can become gneiss if sufficient heat and pressure is applied. Metamorphic rocks can be identified in a number of ways. Those rocks that have been subjected mostly to heat without high pressures tend to have a sugary appearance (like when a wet spoon has been left in the sugar bowl). Rocks that have both heat and pressure have the minerals in layers, this is called foliation. Under extreme pressure the light- and dark-coloured minerals separate into layers or bands.
Questions to answer
Examine the rock in front of you and answer the following questions
a. Is this a sedimentary, igneous or metamorphic rock? (Bonus points if you can be more specific!)
b. What can you see in the rock that tells you the answer to a?
c. Approximately how high is the rock?
d. There are numerous tube-like structures on this rock ranging in size from about 4mm to 20mm. What do you think these are? What do they tell us about the history of this location?
To claim this Earthcache
Email the answers to the four questions to rjm1. Be sure to name this cache in the email as we hope this to be the first of a series.
Logs without emailed answers to the questions will be deleted.
If caching with others, do include each team name in the answers email to prevent their log being deleted.
Don't include any hints or answers in your log.
Please do not include any photographs of the rock in your log. Photographs of your team are most welcome.