Welcome

Welcome to the Little Jerusalem EarthCache Series. This series was placed at the request of the Stae Park so it is important that you follow all rules to demonstrate how responsible geocachers are with the environment. Please stay on the trail and follow all rules as posted.  At no point, should you touch, collect, or disturb the environment except where specifically directed. Please enjoy this series of EarthCaches responsibly. There is a $5 day fee to access this park. 

Earth Science Lesson

At GZ you will be able to observe a large section of rock that has "broken off". Geologists like to be a little more percise when describing such conditions by using the terms cleavage and fracture. Today we are going to learn a little more about those terms and apply them to what you see before you. 

Cleavage / fracture

Cleavage and fracture describe different ways in which a mineral can break.

Definitions

Cleavage - The tendency of a mineral to break along flat planar surfaces as determined by the structure of its crystal lattice. These two-dimensional surfaces are known as cleavage planes and are caused by the alignment of weaker bonds between atoms in the crystal lattice. Cleavage planes are distinguished from fracture by being smooth.

Fracture - The way a mineral breaks other than along a cleavage plane.

Terminology

Cleavage terms (only use if cleavage planes can be recognised):
Perfect - Produces smooth surfaces (often seen as parallel sets of straight lines), e.g. mica;
Imperfect - Produces planes that are not smooth, e.g. pyroxene;
Poor - Less regular.
Non-existent.

Fracture terms (use in all other cases):
Conchoidal - Fracture surface is a smooth curve, bowl-shaped (common in glass);
Hackly - Fracture surface has sharp, jagged edges;
Uneven - Fracture surface is rough and irregular;
Fibrous - Fracture surface shows fibres or splinters.

Logging Tasks

1. Observing the feature, describe the cleavage.
2. Would you describe the cleavage as perfect, imperfect, poor, or non-exsistant?
3. Describe the fracture surface.
4. Would you label it as conchodial, hackly, uneven, or fibrous?
5. Post a photo of yourself, or a proxy, at GZ. (No spoilers please)

References

1. Geology Rocks and Minerals (2005). Cleavage/Fracture. Retrieved from https://flexiblelearning.auckland.ac.nz/rocks_minerals/minerals/fracture.html

2. Minerals.net. (2020). Mineral Properties: Cleavage (Including fracture and parting) Retrieved from https://www.minerals.net/resource/property/Cleavage_Fracture_Parting.aspx