As part of our studies this year in Earth Science, we will learn more about the three
main classes of rock - igneous, sedimentary, and metamorphic rock. This past year
I had the opportunity to visit Sydney Australia. During my visit, I was able to view
one of the most unique and spectacular type of sedimentary rock known as Sydney
Sydney sandstone is the common name for Sydney Basin Hawkesbury Sandstone. It
was historically known as Yellowblock, a sedimentary rock named after the
Hawkesbury River found north of Sydney where this sandstone is very common.
Sydney sandstone dates back millions of years ago to the Triassic Period. The ripple
marks in this sandstone formed from the ancient river that brought the grains of sand
and are distinctive and easily seen.This led geologists to conclude that the sand comes
from rocks formed between 500 to 700 million years ago. Sydney sandstone is
composed of very pure silica grains and a small amount of the iron mineral siderite,
bound with a clay matrix. It oxidizes to the warm yellow - brown color that is
notable in the buildings that are constructed of it.
Sydney sandstone is well known for its durable quality. Since Sydney sandstone formed
the bedrock for much of this region, it was quite plentiful. It was a highly favored
building material, especially during the city's early years. From the late 1790's to the
1890's, it was used particularly in many public buildings in an area of Sydney known
as The Rocks District. These early buildings were built primarily by prisoners sent
to develop the land of the early colony.
I have attached some actual pictures of Sydney sandstone that I took on my visit.
I hope that you will learn some more about the features of sandstone as you take
a closer look at these pictures of Sydney.