The Rock Cycle EarthCache

The Rock Cycle

By Seemyshell

Mill Creek which runs north to south following the firetrail on the western side, once filled this entire area. Evidence of this can be seen in the form of the great rock formation and feature you see at WP2. It is the largest and and most exposed rock wall along the firetrail, and has some wonderful colourings, and shapes. After learning about the rock cycle you should be able to explain why this geological feature is here, and why it has the shapes and colours that it does. 

The Lesson...

Like most Earth materials, rocks are created and destroyed in cycles. The rock cycle is a model that describes the formation, breakdown, and reformation of a rock as a result of sedimentary, igneous, and metamorphic processes. All rocks are made up of minerals. A mineral is defined as a naturally occurring, crystalline solid of definite chemical composition and a characteristic crystal structure. A rock is any naturally formed, nonliving, firm, and coherent aggregate mass of solid matter that constitutes part of a planet.

Sedimentary Rock- Sedimentary rocks are those rocks made up of pieces of other rocks. We call the pieces of rock "clasts" (Clast means "broken piece"). A clast is a piece of rock broken off of another rock. Clasts of rock are eroded from larger rocks, transported (moved) by wind or water and deposited in a basin.After some period of time, the clasts are lithified (lithos is the Greek word for stone). The sedimentary rocks we see today were once gravel, sand, silt, mud, or living things. We decide what to name sedimentary rocks based on the size of the clasts that make up the rock. For most sedimentary rocks, this is easy. Sandstone is made of sand, siltstone is made of silt, mudstone is made of mud and so on. Even volcanic ash can become sedimentary rock! The only hard ones to remember are conglomerate and breccia. Conglomerates are made up of rounded, gravel-size particles (To a geologist, gravel is anything from 2mm to 4 meters in diameter), and breccia is made up of angular, sharp-edged, gravel-sized clasts. Limestone and chert are classified as sedimentary rocks, but most limestone and chert are grown by living organisms rather than broken from other rocks. Some limestones have fossils, but most limestones and cherts have recrystallized, and the remains of the creatures that made them are no longer visible. 

How to log this earth cache

After Learning about the Rock Cycle and looking at the Geological Feature in front of you, you will need to answer the following questions. Please send the answers my way of GC message or email to the CO. Feel free to log your find, and I will contact you if I need to clarify any answers.

1- At WP2 - What type of rock are you looking at? Sedimentry, igneous, or metamorphic?

2- Explain your answer to Q1?

3- What colours can you see, and how are these colours formed?

4- What evidence can you see that would allow us to come to the conclusion that the water from Mill Creek used to flow up here.

5- Give an estimation of how high above the current water line you are standing at WP1. (This shows how much the water has subsided over time).

6-  WP1 - What evidence do you have that shows the Rock Cycle? 

7- (Optionable) Upload a photo of yourself or your GPS at WP2, showing the colouring and weathering of the rock face.

Did you know that NSW has a geocaching association? Geocaching NSW aims to enhance and improve the activity of geocaching and holds regular events where geocachers meet to enjoy their common interests. Visit the association website here.