Sand seems to be everywhere…it’s on the beach, it’s in the rivers, it’s in the dunes, its in the deserts and for some folks, its on their farms! Some of this sand is unconsolidated (loose stuff), while other sand has turned into rock – called sandstone. So what is sand and what does it mean for my farm.
I grew up in Sydney, Australia. All the rocks around our place was a beautiful type of sandstone – a yellow quartz-rich stone that made up many of the old convict built buildings.
Our first farm in Colorado was built on an old sand dune. The sand came from wind blowing sand around at the end of the last ice ages. This sand accumulated on top of the rocks surrounding Denver, and close up to the Rocky Mountains. The sand had also been washed out of the rocky mountains during large floods. Which ever way – it was sand (and lots of it!).
What is sand?
Sand is actually just a size of grain. It starts at around 2 millimeter and goes down to around 1/16 of a millimeter (ok – for the non-metric folks…there is 24.5 mm in an inch. So American friends, a grain of sand is about the thickness of quarter down to a particle so small that it can only just feel it between your fingers).
What is sandstone?
As well as the sand grains, sandstones contain a material that cements the grains together to form the rock. This cement is normally one of three minerals – silica (or quartz), calcite or an iron oxide. These two are important as when the sandstone breaks down they can remain in the material that makes up your soil.
So how do sandstones affect my soil?
Knowing what type of sandstone occurs on your property will tell you something about the types of soils that will develop on your farm. So we go back to the table of what minerals the rock contains and what materials you will end up with:
|Original Mineral||New Mineral||Released Elements|
|Felspars||Clays||Potassium Sodium Calcium|
|Iron Oxides||Clays||Iron Magnesium|
|Calcite & Dolomite||Calcite||Calcium Magnesium|
Generally speaking, a quartz sandstone is going to produce very poor soils – as quartz does not weather to another useful mineral. So you basically get sand with very few clay minerals. This is so true of the soils in my family home in Sydney and my farm soils in Colorado!
Arkose sandstones weather to produce soils richer in clays as the feldspars weather to form clay. These can end up being some of the best soils once loads of organic materials is added.
Calcarious sandstones contain the mineral calcite (calcium carbonate). Some of them are so rich that they are almost limestones (you can read about limestone and what it means for your farm here).