This is a park and walk cache. Depending where you park the walk is between about 100 and 300 metres each way.
Please park at Lilydale lake or the in the clinic car park listed.
Please do NOT park on the roundabout or main road.
You should now be standing in front of a rocky outcrop which is part of the north western tip of the Dandenong Ranges.
There are 3 main categories of rock in the earth - igneous, sedimentary and metamorphic – and mostly it is not difficult to tell which is which. They are connected to each other in the rock cycle, and move from one type to another, changing shape, structure and sometimes their chemistry.
From The Rock Cycle
Igneous rocks
These are formed from molten magma beneath the earth’s surface, or on the surface as lava eruptions as they cool. In cooling their mineral grains bind together tightly, and so they are quite hard and strong rocks. Igneous rocks make up a large part of Earth's crust. Examples are granite, basalt (bluestone), and obsidian.
They are made of primary minerals and are mostly black, white or grey. Their textures can be smooth and shiny. Tiny, crystalline particles in the structure of a rock may mean it is igneous.
Sedimentary rocks
These rocks are formed by the accumulation of small particles or sediments from the breakdown of other rocks. These sediments are called clasts and can be carried by water or wind and deposited in a different place. Over thousands of years, they get compressed to form mudstones, sandstones, shales and conglomerates.
Other types of sedimentary rock are formed from the remains of plants or sea animals, which become coal, limestone and chert.
Generally sedimentary rocks are seen in layers (strata). They are usually the colour of sediment - light sandy brown to light gray. They may contain signs of life such as fossils, and animal tracks, as well as water ripple marks. They are much softer than igneous rocks.
Metamorphic
Metamorphic rocks are formed from the other rocks by the effects of heat, pressure, fluids and strain; for example when tectonic plates move and create mountains; and from the heat of volcanic activity. Igneous rocks can be reheated and changed; and sedimentary rocks can be compressed into other rocks such as quartzite, schist and gneiss. When sedimentary limestone recrystallises under pressure, it can become marble.
Due to the high heat and pressures that create them, these are mostly very strong, hard rocks. They're made of different minerals to other rocks and have a wide range of colours and lustre. They may show signs of stretching or squeezing, giving them a striped appearance.
Appearances can change
Rocks can change their appearance because of weathering, the intrusion of other minerals such as iron or copper, and as a result of human activity. There is a good example to such a change at the left side of the outcrop.
Questions
By examining the outcrop, and using the information above, please answer the following questions to complete this cache, and message the answers to the CO. You can log the cache immediately. Please note you can only answer all these questions correctly by visiting the GZ. The photo does not show all the features you need to examine.
- From the 3 types described above, what type of rock are you looking at ? And what are the reasons for your answer?
- Do you think this rock face is natural or caused by humans? And what are the reasons for your answer?
- What might have caused the discolouration on the left of this outcrop ?
- Did you find any tiny crystals on this rock face ? And if so where? You can send a photo if you like, and this is optional.
Thank you for visiting this cache. FTF honour goes to ahomburg on 6 -11-18
References
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