What Is Sandstone?
Volcanic rocks did reach the surface and usually flowed. Metamorphic rocks are any rocks that have been subjected to deforming temperatures and pressures. The main constituent of all sandstone is grains of quartz. The quartz is stuck together by a natural cement of clays and traces of other minerals. So if you took a ‘thin section’ of sandstone and looked at it under a microscope, you would see grains of sand with a cement matrix. Helidon Sandstone is mainly ‘fine’ to ‘medium’ grained, which means the grains of sand are relatively fine and hard to see with the naked eye. Coarse-grained sandstone can be found in Helidon but has a rougher texture to the hand.
When And How Was Helidon Sandstone First Deposited?
Helidon Sandstone was deposited in the Upper Triassic to Lower Jurassic, which makes it about 200 million years old (in a range from 210 to 190 million years). The sandstone was deposited in a fluviatile environment, which means rivers and estuaries. This was a freash water enviroment. A landmark of a fluviatile deposit is ‘cross bedding’ and you can see examples of this in road cuttings as you travel between the towns of Helidon and Gatton and of course in the quarries at Helidon. Bedding defines how the rock was originally deposited. Because rivers often flood, you often find bands of boulder or shade within the beds. This reflects turbulent times or very quiet times in the river deposits.