What is Sandstone made out of?

Lion’s Head Stone – Nambia

We at Stonehenge Walls use Sandstone in the construction of our retaining walls, but have you ever wondered how they are made and what they are made of? Given that we use it every day we wanted to find out.

The What

Basically all rocks in the world are made primarily of the element Silicon. Silicon is our 3rd most common element (after Iron and Oxygen). Given that almost all the Iron is in our molten core and the Oxygen is captured in water and air it makes sense that all that is left for rocks is Silicon. Silicon itself is a very versatile element, it’s raw elemental form makes it look like metal, but throw in some heat and oxygen and it turns into Quartz. Add a little Sodium and Aluminium (or a few different combinations) and your Quartz now becomes a¬†Plagioclase Feldspar, or a complicated word for what makes up the base of all rocks.


Now if you’re still with us after that science lesson, we can talk about what Sandstone is actually made up of. Most Sandstone is made up of crushed Quartz and Feldspar. A cool result of this is Sandstone becomes extremely weather resistant. Have you ever noticed how Sandstone walls and buildings don’t seem to change after decades? That is because as Sandstone is water permeable (as in soaks in water and lets it pass) anything that could be picked up by water already has and you’re left with an extremely resistant rock. Which is exactly why we use it at Stonehenge Walls to build our stone retaining walls.


Colour is determined by what is in the area when the stone is quarried. Iron Oxide turns Sandstone red and given Australia’s huge iron reserves it makes sense that most of our sandstone is yellow to red. Purplish Sandstone exists for example, and is caused by the addition of Manganese while the stone was forming. You can even get blue Sandstone if there is a significant amount of Silt and Clay where the sandstone is found.

The How

Sandstone is a sedimentary stone. That is a type of stone that is formed over time with new material being added to the top constantly in layers. This means a volcano didn’t explode and form sandstone, it took a long time. Once the material, normally Sand for Sandstone, has stopped moving it is given the chance to compact down. With enough time and pressure, along with a natural cementing agent such as calcium carbonate (Shells of marine animals, snails and eggs) or Silica (Oxygen and Silicon) it forms the stone.

The most common places for Sandstone to form naturally are Old Glaciers, Rivers, Lakes, and Deserts. Places that provide a huge amount of pressure and are relatively stable. It is commonly thought that the Ocean floor is almost entirely made out of Sandstone for the obvious reasons of having access to huge amounts of Calcium Carbonate (shells of marine animals) and the huge amount of pressure the ocean provides. It would be very interesting to see that stone used in Retaining Walls.