Before You Attempt
Access to the lime kiln is not possible during lambing (Sept / Oct).
You will need to bring some weak acid (eg vinegar) to complete the logging task.
A traditional cache (Lemon and Lime GCN42X) used to exist here; indeed this was one of the prompts that got me into caching. It is an interesting site, with some excellent views, and both geological and human history values. Just a bit too popular for a physical cache to avoid multiple mugglings...
Geological History
Between 75-13 million years ago the Dunedin area was covered by the sea. Beds of broken shells built up and over time the shell fragments were compacted by their own weight (and the water above) and were concreted together from minerals in seawater to form limestone.
During the period of volcanic activity of 13-10 million years ago the limestone in this area came into close but not direct contact with molten magma. In a process called contact metamorphism the heat of the molten rock caused partial baking of the limestone so that its structure is changed from how it originally looked. You will see that it is certainly nothing like Oamaru limestone! It is also nothing like the metamorphic marble that you would end up with from more heat and pressure.
If anything fits the archetypal shape of a volcanic cone it must Harbour Cone the obvious hill in the distance beyond the lower kiln. Surprisingly, it is in fact just rock with a hard diorite cap. The surrounding weaker material has eroded away from, forming a cone shape in the process. So, though diorite is a volcanic rock, no lava ever erupted through Harbour Cone.
Lime Kilns
The kiln below the road was built in 1865 by a Scotsman named McDonald. During the 19th century lime was burnt in small kilns like this. Limestone was extracted from the quarry above the kilns and was loaded into the top of the kiln via a gantry (long since gone) and burnt. Limestone, which is mainly calcium carbonate (CaCO3), was burnt to drive off carbon dioxide (CO2), leaving calcium oxide (CaO) - otherwise known as burnt lime. Crushed limestone was used to improve pastures, and burnt lime was used to make mortar. In 1976 New Zealand Cement Holdings gifted the lower kiln, together with the adjacent limestone quarry to the Otago Peninsula Trust. Restoration work began and was supported by the NZ Historic Places Trust. The lime kiln is protected and maintained by the Otago Peninsula Trust and is open to the public to view.
Logging Tasks
1) Locate: a piece of semi-baked limestone from above the kiln. Test that indeed it is limestone by placing some acid on it in the following reaction:
acid + limestone --> salt + water + carbon dioxide
Vinegar (contains acetic acid) will be a good household source of weak acid. The impact of this reaction is less than minimal but please don't use anything stronger.
The acid will react with the limestone to evolve carbon dioxide (seen as bubbling and fizzing). Upload: a picture of the test being carried out with your GPS in the picture for authentication.
2) Count: the number of metal tubes sticking out of the kiln. Given the information above about how lime kilns work please infer how these help with the functioning of the kiln.
Logs not complying will be deleted.