What is Granite:
Granite is an Igneous rock which is one of the three main rock types. Igneous rock is formed through the cooling and solidification of magma or lava. Igneous rock may form with or without crystalization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. The granite at the Sturt Reserve is classed as intrusive as it is thought to have formed many kilometres underground.
Local Granite:
The local granite outcrops around Murray Bridge are part of an extensive series of batholiths as seen on the map at the EarthCache site. A batholith is a large emplacement of igneous intrusive (also called plutonic) rock that forms from cooled magma deep in the Earth's crust.
These rocks formed as a consequence of a widespread mountain building episode called the Delamerian Orogeny, which occurred between 515 and 495 million years ago. During this event the crust was squeezed and became much thicker and hotter. As a consequence molten material was produced deep within the mountains. The granite has been brought to the surface here by erosion and uplift over the millions of years since they were formed.
Minerals:
The granite in Murray Bridge is composed of three main minerals.
They are quartz, feldspar and biotite mica. The minerals which comprise the granite form the crystalline structure as the molten material cools over many millions of years. The longer it takes to cool, the larger the crystal size in the rock.
Now on to the questions. It may help to print off this page when you do the Earthcache.
Q 1) What are the colours of the three main minerals
Quartz- Colour ( ) Size( )
Feldspar- Colour ( ) Size( )
Biotite Mica- Colour ( ) Size( )
AND looking at the granite itself what size crystals are the minerals, eg Small, Medium or Large.
Q2) After working out the size of the different minerals, what does that say about the length of time it took for each to cool? Which mineral took the longest time to cool and why?
Q3) How many tonnes of granite form the Adelaide Railway Station buildings? Tonnes.
Send the answers to us using our geocaching.com account. You may log your find at the same time you send the answers, but if we do not receive any answers we will delete your log as per the Earthcache guidelines.