Rocks soil and minerals – it sounds like you are back in 8th grade science at school – but now all that great information about rocks soil and minerals is going to come back and help you understand more about the most vital component of your homestead – the material in which you want to grow your fruit trees, hay, vegetables and more.
The soil minerals component of our soil is so important but often overlooked as we strive to improve our soils through adding organic material via composting. But it is the soil minerals that provides most of the vital elements needed for plant growth.
Rocks soil and minerals
To understand soil minerals means we need to have a basic understanding of the rocks that underly our farms. Most of the time these rocks are not seen as they have a layer of soil and/or vegetation on top of them. And the rocks you find on your place may be “visitors” that travelled in glaciers and were dumped there during the last ice age. This is especially true in the upper states of the USA and into Canada. No matter what the situation is, you should check around and see what rocks you can find on your farm.
Quick rock primer
All the rocks on our planet can be divided into three major groups.
Igneous rocks – are those that formed from the cooling of molten rock either below ground (plutonic rocks like granite or gabbro) or above ground (volcanic rocks like basalt or rhyolite)
Sedimentary rocks – are those formed from the cementing together of cobbles, sands, silts or mud size particles into layers of rocks. Most of these are formed in the oceans on the margins of the continents where these materials have have washed from the land in rivers such as sandstone, shale, conglomerate or built up from the remains of animals like limestone.
Metamorphic rocks – these are the squashed and/or cooked (but not melted) remains of any rocks that have been in locations of mountain building, continents colliding or close to huge masses of molten material. Rocks like schists and marbles, quartzites and gneisses.
All these rocks are made up of a mix of the common minerals.
Quartz, Felspars, Mica, Amphibole, Pyroxene, Olivine and Calcite. And there are then a splattering of minor minerals.
Here is a table of just a few of the common rock types and the minerals they contain:
|Rock type||Rock Name||Minerals|
|Igneous||Granite||Quartz Feldspar Mica|
|Igneous||Rhyolite||Quartz Feldspar Mica|
|Igneous||Basalt||Amphibole Feldspar Pyroxene Olivine|
|Sedimentary||Sandstone||Quartz Feldspar Mica Clays|
Once a rock is exposed to the weather it will start to break down “physically” into smaller grains and “chemically” into different minerals. These major rock forming minerals break down into the following minerals you will find in your soils:
|Original Mineral||New Mineral||Released Elements|
|Felspars||Clays||Potassium Sodium Calcium|
|Calcite & Dolomite||Calcite||Calcium Magnesium|
So combining these two pieces of information together it works like this. If you you live in an area where granite is the dominate rock type (a rock containing quartz, feldspar and mica), you will find your well developed soils contain quartz grains and clays. In less developed soil, it will appear sandy as the feldspars may not yet broken down into clays. The soil will contain potassium, sodium and calcium.
If your homestead is on basalt, you will have clay rich soils with loads of iron and magnesium.
The best way to find out what rocks you have in your area is to visit your national or state’s Geological Survey. To find those in the USA go here (http://www.stategeologists.org/). They will have maps (many online) and advice to help you discover whats under your feet.
USGS Minerals in the Soil Maps
From 2007 to 2009 the USGS began sampling soils in the lower United States as part of the North American Soil Geochemical Landscapes Project. They took samples at a depth to 2 inches (5 centimeters)..basically to represent the A horizon in the soil, and a deeper sample at around 3 feet (1 meter) to test the lower soil profile (C horizon). They then analyzed these samples and created this amazing maps for the major minerals in your soil.
Below are some of the major soil minerals. You can click on the link for the interactive maps – you can see the C horizon samples as well as overlays of geology etc.
Here is the link to the USGS interactive map for Quartz
Feldspars come in two major types – potassium rich feldspars (such as the oink Orthoclase) and Sodium-Calcium rich feldspars (the Plagioclase minerals). The USGS have separated these.
Here is the link to the USGS interactive map for Potassium Feldspar
Here is the link to the USGS interactive map for Sodium-Calcium Feldspars (Plagioclase)
Here is the link to the USGS interactive map for clay
Calcite is calcium carbonate.
Here is the link to the USGS interactive map for calcite
Dolomite is a magnesium rich carbonate.
Here is the link to the USGS interactive map for dolomite
So what can you do to find out about the rocks soil and geology on your farm?
To get a general idea of what rocks soil and minerals you will find in your area, the best way is to walk around your farm with someone who can identify what you have. I know this is not always possible – and so getting at least a geological map of your area is a great start. Your country or state/province will have a geological survey that can provide you a map. There are also some great online resources. Below are some great links to help you out:
Sources of information for rocks soil and geology on your farm: