In Ambers Gully a section of ancient quartzite forms a cliff across the gully. The stream tickling down from above has formed a strange and unique "frozen" waterfall. Looking like a twenty metre high distorted toadstool, the feature is a rare extensive formation of tufa, a calcite deposit that has been created over thousands of years. Calcium has been leached out of the hills above, and the rarely running creek has trickled over the brink of the cliff. The sun has evaporated the water flow, and crystals have deposited and added to the unusual phenomenon. Alongside the current falls are weird, bulbous formations looking like overlapping stone umbrellas, all formed in the same way.
Quartzite is a metamorphic rock derived from sandstone. Heat and pressure combine to fuse grains of quartz sand to make up the composition of quartzite. The mineral has a uniform texture and is hard, 7 on the Moh's scale. Quartzite is resistant to weathering. The band of hard quartzite at the location in Amber’s Gully has formed a 20m high cliff.
Tufa is a porous rock formed as a deposit from springs or streams. Tufa is a variety of limestone precipitation of carbonate minerals from ambient temperature water bodies. Tufa is a soft mineral, less than 3 on Moh’s scale. Typically calcium carbonate forms the internal formations of caves. At the earthcache location a much rarer external formation has occurred. The restricted water flow of the Ambers Gully stream has also limited the erosion of the tufa formation.
Your earthscience task is to describe the following five physical properties of tufa and quartzite minerals.
- Colour
- Streak
- Crystalline Structure
- Lustre
- Odour