Stanthorpe Rocks! EarthCache
-
Difficulty:
-
-
Terrain:
-
Size: 
(other)
Please note Use of geocaching.com services is subject to the terms and conditions
in our disclaimer.
Stanthorpe Granite
The Stanthorpe Granite was originally a molten mass of magma that rose up and pushed into the older rocks surrounding it, about 240 million years ago (Triassic period). As the magma rose, it melted the surrounding rock and assimilated fragments of it into its mass. Some of these fragments (xenoliths) can be seen today, captured within the granite. Some xenotliths are made of a softer rock than the surrounding granite. When exposed to weathering, these erode more quickly and become recessed. Xenoliths made of a harder material that is more resistant to erosion may protrude from the granite surface.While it was still deep below the Earth's surface, the magma cooled very slowly, allowing its minerals to solidify and grow into large crystals. The crystals interlocked as they grew, creating the coarse-textured granite. These crystals are so big that they can easily be seen in the rocks.
Composition
Granite is an aggregate of silicate minerals. The main minerals in the Stanthorpe Granite are:
Potash feldspar a chalky, light brown-pink mineral with fine straight parallel cracks running through it.
Quartz a very hard, glassy light grey or clear and colourless mineral.
Mica a shiny, black, flaky mineral that sparkles in the sunlight.
Hornblende a shiny, black mineral.
Erosion
Erosion has gradually removed the vast quantities of older rock - a layer maybe three or more kilometres thick - that was once above the Stanthorpe Granite. It is thought that the granite was eventually exposed to the open sky by about 190 million years ago (Jurassic period). Since then, a considerable thickness of the granite itself has also been removed by weathering from above the present land surface. Vast volumes of sand, derived from the eroded granite, have been shed into surrounding areas. The creation of Stanthorpe's landscape hasn't stopped. Wind, water, ice and plants continue to sculpt the granite, as they will for many more millions of years to come.
Question 1
Stand at the lookout, there is a large granite flat in front of you. What do you think the composition of this granite is? ie What percentage is Quartz, Feldspar etc.
Question 2
What surface discolouration is there on the granite flat and what do you think caused it?
Question 3
There is a block made from rock at the lookout. Do you think the block was sourced locally or from another area and why?
Question 4
How tall is the largest granite boulder at this lookout ?
Question 5
Between the lookout and the bitumen there is a sandy patch. What granite component do you think it mainly comprises of?
Optional
Take a photo of yourself at the lookout.
To log this cache you must email the answers to the questions to the cache owner (please include the cache title and do not post answers in your online log) and you can log the find straight after. This earthcache is not about getting the questions perfectly correct, but having a think about the answer and making an informed estimate at the answers. If there are any issues with your answers, I will let you know.
Additional Hints
(No hints available.)
Treasures
You'll collect a digital Treasure from one of these collections when you find and log this geocache:
Loading Treasures