A unique spherical boulder near Killcare, NSW
17 May 2015
This naturally formed spherical rock is located beside the ocean at Killcare.
It was discovered by Benn Miller in 2010. He named it the "Killcare Gobstopper".
The boulder is made of sandstone and is approximately 45 centimetres in diameter. Assuming a density of 2.5, this would make its mass about 120 kg.
It is trapped on all sides by a "cage" of rocks. This cage allows the surging waves in to spin it around, but does not allow it to escape.
A close-up of the boulder.
A view down into the crevice where it is located.
A view from the side.
A view from the front.
The chamber where the boulder was formed.
It is very difficult and dangerous to climb into the chamber and it is only possible at a very low tide.
Nearby there are a number of other partially round boulders of various sizes. The one at the rear of this photo is approximately 1 metre long.
Update - Jan 2016
I visted this spot again, and there is another rock in the "cage" now.
Update - Dec 2016
Update - Dec 2018
By placing a coin on the round boulder, then taking a photo, I estimated that it now has a diameter of about 36cm. This would mean its weight is now around 60kg, which is about half the weight it was when I first measured its size in 2015. So, at this rate of erosion, it may last up to another 14 years.
Update - Dec 2019
By placing another coin on the stone, then taking a photo, I estimated that it still has a diameter of about 36cm
Update - Feb 2023
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