Important
You will need to take some household items to EGZ.
Please read the whole listing before you attempt.
Background
Brighton marks the edge of the Otago schist peneplain and the beginning of the Dunedin volcano complex. Schist is a major feature of the geology of the Otago region. It forms an approximately 150km two sided arch with prehnite-pumpellyite facies nonschistose greywackes on its flanks and greenschist facies rocks in the centre (of course, you say!). Schist is a metamorphic rock formed under heat and pressure applied to existing rocks (often shale or slate). The peak metamorphism of the Otago schist occurred 170-180 million years ago. The schist rocks reached the Earth's surface about 100 million years ago. Widespread erosion occurred reducing the schist to a flat plain at near sea level - once this state is reached further erosion is inhibited (now a peneplain).
The individual mineral grains in schist are drawn out into flaky scales by heat and pressure. These can be seen by the naked eye and can appear as page-like layers. Schist is characteristically foliated, meaning the individual mineral grains split off easily into flakes or slabs. Indeed the greek word schist is derived from means "to split."
Mohs hardness scale is a means of identifying minerals based on their hardness. It is based on the ability of a mineral to scratch another. The material that was scratched is softer than the one that did the scratching. Mohs scale ranges from 1 (most soft - eg talc) to 10 (most hard - eg diamond). A series of scratch tests using different materials will reveal the hardness of a mineral and hopefully its identification. Note that the scale is not linear (8 is not twice as hard as 4).
Scratch test in action (the nail is harder than the limestone) - Source: www.saltthesandbox.org
At EGZ you are expected to carry out a scratch test and identify one mineral from the schist rock as best as you can using the mohs scale. Study the links to the common Otago schist minerals of quartz, feldspar, biotite and chlorite to help in this (Links contain mohs hardness for each).
Useful commonish items that you could take to EGZ in order to do the scratch test:
1.5 Pencil lead (actually graphite), tin, lead
2.2-2.5 Fingernail
2.5 Gold (24 carat)
2.75 Aluminium
3.0 Chalk (calcium carbonate)
3.2-3.2 Ten cent coin
5.1 Pocketknife blade
5.5 Glass
6.5 Steel file
7.0 Unglazed porcelain, garnet sandpaper
9.0 Common sandpaper (artificial corundum)
9.0-9.5 Tungsten carbide (hardened cutting tools)
10 Diamond
Mohs Scale - Source: www.elearning.stkc.go.th
Logging Requirements
0. Preface any email with GC3RNJ4 Scratching Rocks in Brighton in the subject line and title and clearly note the question number and answer. Do not wait for a confirmation email to log but be prepared to be asked for additional information if your answers are slim.
1. Report the colour of the mineral you chose to scratch test
2. Report your Mohs hardness for the mineral you tested
3. Report which item your mineral scratched and which scratched it
3. Report which mineral it is that you think you have identified
Email answers to gcstegan"at"gmail.com
No photo is necessary but please make sure your answers are correct or your log will not be valid.
2012 Stegan's EarthCache Masters Programme
It is not very feasible for many New Zealanders to get past the Bronze level on the earthcache.org programme becase you need three states for Silver which means leaving the country! So, as in 2010 I've decided to run a little sideshow on my new earthcaches this year... with the following points system:
5 points: First to find
3 points: 2nd to find
1 point: Logging a find
1-5 points: Special bonus questions.
At the end of 2012, I'll issue certificates for 1st, 2nd and 3rd.
Updated information and Leaderboard at: Stegan's Earthcache Programme
