The location of this earth cache is two large granite boulders that have been brought to Adelaide from some considerable distance. Your task at the earth cache site is to learn more information about the type of minerals that make up these boulders and their source.
Granite rocks are plutonic igneous rocks, which were formed by slowly cooling pockets of magma trapped beneath the earth's surface. Granites are typically a hard rock with visible crystalline texture, rich in quartz and feldspar. Granite is the most common igneous rock of the Earth’s crust. An outcrop of granite on the earth's surface requires some kind of erosion to expose the buried material.
The granite boulders on display are a matched pair that have been selected and transported to the site. The boulders at the cache location are distinctly different minerals known as Pegmatite and Charnockite. Please identify the source location of the individual boulders. Describe the structure and morphology of each boulder. Specifically comment on the variations in physical attributes that are apparent and the crystal size of the individual boulders.
Crystals are produced whenever a solid is formed gradually. Granites are crystalline rocks. If the granite source material, magma, is cooled rapidly, numerous seed crystals form and grow only into tiny crystals; but if the material is cooled slowly, a few seed crystals will grow into large crystals. To study the crystal structure and colour of the boulders it may be useful to wet the surface. Water is available at a nearby water fountain. Alternatively you may lick a rock surface to show the crystal structure and colour.
To claim this earth cache you need to have the following earth science details validated by email.
:-Identify the original locations of the granite boulders. Identify the distance travelled by the furtherest boulder.
:-Describe the boulder features; size shape and crystal structure. Explain why the crystal structure is different.
:-Post a photograph of yourself with your GPS showing the nearby bust.
You are encouraged you to comment on what you enjoyed or found interesting at the location when logging your visit.