The geology of Hanging Rock is volcanic. It is known as a Mamelon, created more than 6 million years ago by stiff magma oozing from a vent and congealing in place. As it cooled it split into rough columns and has been subjected to weather erosion ever since. This type of geology is only found in this area and in Norway and Sweden, known as Solvsbergite or soda trachyte.
Here is my approach to the rock.
Hanging Rock, Victoria 718 Metres (2356 Feet)
Click the image for a larger view.