There is no physical container at the published coordinates. This is an EarthCache. To find this cache you must visit GZ, make some observations, and send your answers to the cache owner.
At GZ you will find the Marulan Town Clock - but you may not notice the actual clock at first, because it sits atop a huge boulder. This boulder is in fact the largest piece of limestone ever transported by road in the Southern Hemisphere. It has been here since 1991 and weighs 30 tonnes - and apparently broke the transporter that brought it here.
This massive boulder is interesting not just for its size, but also for its composition and appearance. We can roughly divide its composition into a darker grey material and a lighter white material. But these are both limestone - a sedimentary rock composed of calcium carbonate in several crystal forms. So why do they look so different?
The dark material is the host rock, formed millions of years ago, likely in a marine environment. It consists of microcrystalline calcite (or micrite) that is formed from compacted shells, mud, fossils and other sediment, piling up over millions of years and compacting into limestone. Because it was formed in this gradual way over time, it contains impurities such as organic matter, clay particles, iron or other minerals that were deposited into the sediment. These impurities have affected its colour.
The lighter material is much newer calcite. This formed long after the original limestone hardened, so it's called secondary or post-depositional calcite. The original limestone experienced stresses which fractured the rock, leaving cracks which later filled with water rich in calcium carbonate. As the water moved through the rock, the dissolved calcium carbonate precipitated out and filled the fractures with relatively pure crystalline calcite. If you look at the stone from a distance you can clearly see the lighter veins form a lattice of continuous fractures through the darker host rock.
There is also iron oxide in the rock, adding a splash of rusty orange-gold colour. This may be from the original sediment including small amounts of iron-bearing minerals, or dissolved iron may have been introduced by water moving through the rock over time. As these minerals have been exposed to oxygen and water in the air, they oxidize, giving the rusty colouring.
Finally, there are circular fossils in several places on the rock. These are likely from sponge or tube corals, the hard stems of which were embedded in the original stone, then were fossilised over millions of years and replaced once again by relatively pure crystalline calcite. Where the rock has weathered or split across the fossilised stem you can see the resulting circular cross-section.
To log this EarthCache:
You must visit GZ, make some observations, then email or message me your responses to these tasks:
1. Examine the darker stone and the lighter stone. Find a thick vein of the light stone and compare the crystals there with the nearby dark stone. Which type of stone has larger, more easily-distinguished crystals?
2. The lighter veins cut through the darker rock - but do they also cut through the iron oxide sections? If so, we can assume the iron was in the original sediment. But if the iron oxide cuts through the dark stone and the light stone, we can assume it was introduced to the stone later than both. What do you think?
3. Find a circular fossil - there are good examples on the far left side and the right-back side as you face the plaque on the stone. Roughly how big is the fossil? How do the white crystals here compare with the white crystals in the thick vein you observed earlier? What might this tell us about how both sections were formed?
4. Finally, take a photo of yourself or a personal item, showing the Marulan Town Clock in the background at the time of your visit - the actual clock please, not the boulder! Please attach this photo to your log.
You may post your Found log immediately without waiting for my response. I may not contact you unless I feel your answers require clarification. If I don't receive your correct answers within 7 days of your Found log, I may delete your log. Please don't post answers to the questions above in your log.