The mottled rocks in the cliff in front of you look like a sandstone but an acid test proves that the mineral contains carbonate. Analysis of the two phases confirms that the darker phase is carbonate rich phase, and the lighter colour is carbonate poor limestone.
Dark Phase
Calcite ~95%
Quartz ~5%
Light Phase
Calcite ~40%
Quartz ~20%
Muscovite mica ~30%
Kaolinite ~5%
K-feldspar ~5%
The Australian Stratigraphic Units Database identifies the mineral as Parara Limestone: nodular limestone with minor mottled argillaceous limestone and thin calcareous shale. The mottled texture is found in carbonate mineral from the early Cambrian. It is probable the material formed in oscillating aerobic-anaerobic conditions below the sediment/water interface. The textured limestone features have been seen in three distinct forms: ribbon, nodular and mottled. The first two forms show evidence of bedding (layers). In the third mottled form bedding is poorly developed. Observation at the cliff shows a changes in form.
To log this earthcache you will need to measure and observe the mottled rock on the cliff.
The dark colour is grey. What colour is the lighter phase? Why do you think you can see different lighter colours?
Optional Task
Can you thread the eye of the needle?