Minerals

Minerals are in that category of things you feel pretty sure you know what they are until you start digging.

Pure calcium in a protective argon atmosphere (Matthias Zepper) Public Domain

What are minerals?

In my mind’s eye, I always thought of minerals as tiny rocks, but I was only partly correct. Rocks are relatively homogenous, solid geologic materials. Rocks may consist of one mineral or be an aggregate of several minerals. According to the dictionary, minerals are “solid inorganic substances of natural occurrence” which coincides nicely with my rock theory. More accurate definitions describe minerals as well-defined chemical compositions with specific, naturally occurring crystal structures. My tiny rock theory is okay up to this point, but this is where it starts getting tricky.

Mineral species

Did you know that there are different mineral species and varieties? I didn’t, either. One tiny difference in the composition of a mineral changes it completely. Common quartz becomes amethyst when impurities turn it purple.

Quartz crystal (JJ Harrison) CC BY-SA 2.5

Amethyst (Gonzalo Devia) CC BY-SA 4.0

Other minerals are biogenic. Biogenic refers to materials made from or by living things. Calcite of chalk and limestone fame is a biogenic mineral consisting of the bodies of tiny algae, fairy shrimp, oyster shells, and other marine organisms.

Calcite occurs in many forms (PaleoNeolitic) CC BY 4.0

The rules about mineral classification are not set in stone, however. Opals and obsidian seem to meet the mineral criteria but don’t quite make the cut. They are mineraloids. I have no idea why.

Organic minerals

Other minerals are classified chemically as organic compounds. These minerals are organic in the sense of being related to living material. For example, mellite is a mineral made from plant material. And the carbon that makes up all life on Earth is also in this category. The carbon cycle transforms inorganic compounds into organic ones. Of course, scientists are still debating about where the line between organic and inorganic lies, but we’ll leave that line in the sand to them.

Potassium (Philmason thunderf00t) CC BY-SA 4.0

Garden variety minerals

Plants use minerals as food. When they use relatively large amounts, we call them macronutrients. Nitrogen (N), phosphorus (P), and potassium (K) are the Big Three macronutrients but plants also use large amounts of calcium (Ca), magnesium (Mg), and sulfur (S). Plants also consume tiny amounts_of micronutrients like boron (B), chlorine (Cl), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), nickel (Ni), and zinc (ZN). These minerals naturally occur in the soil. And there’s only one way to find out what’s in yours. That’s with a lab-based soil test. These tests are inexpensive. They provide the information you need to feed your plants correctly. Unfortunately, those cute plastic test kits from your local garden store are not yet accurate enough to be useful.

Too much fertilizer can cause some minerals to reach toxic levels, creating more harm than good, especially with boron, chlorine, iron, and manganese. Soil can also contain high levels of aluminum (Al) and sodium (Na) which interferes with plant growth.

As of November 2020, the International Mineralogical Association (IMA) recognized 5,863 unique minerals on Earth. Of those, nearly 500 minerals came from somewhere else.

Now you know.