There are many ways to identify minerals. Here, let’s look at simple techniques that you can use for identification in the field. We will discuss identifying volcanic glass and lithic fragment, too, even though they are not minerals.
Minerals containing iron (ferrous iron: Fe2+) demonstrate magnetic properties. The higher the iron content is, the stronger the magnetism. So, here we will introduce a classification method utilizing two types of magnets.
| Minerals attracted to normal (ferrite) magnets (highly magnetic minerals) | Magnetite |
|---|---|
| Minerals attracted to strong magnets of Samarian cobalt or neodymium iron boron (weakly magnetic minerals) | Garnet, Orthopyroxene, Clinopyroxene, Amphibole |
Once they are stuck to your magnet, minerals are extremely hard to remove. Cover the magnet with a plastic bag first, for easy cleanup!
Take care not to get strong magnets too close to magnetic strip cards (like cash cards) or cellular phones—they can cause malfunctions. Be especially careful if you have a pacemaker or other medical device that could be affected.
This is analysis with the naked eye, though a 5x hand lenswill come in handy. Basically, any magnifying glass will do, but a mineral or jewel hand lens is ideal.
| Shape | Mineral |
|---|---|
| Prolate (Rod shaped) |
Quartz, amphibole, plagioclase, epidote |
| Bladed (Elongated and flat) |
Orthopyroxene, clinopyroxene |
| Planer (sheet-like) |
Muscovite, biotite, chlorite, serpentine |
| Equant (Spherical or cubic) |
Garnet, olivine, magnetite, pyrite |
| Irregular (many are angular) |
Volcanic glass, lithic fragments |
Shape is only a rough guide to identification; some minerals will have been broken, losing their original shape, through the process of transportation and sedimentation.
Light minerals are generally colorless, while heavy minerals have color. The majority of minerals are translucent, but some heavy minerals are opaque. These are known as the opaque minerals.
| Colorless | Quartz, feldspar, volcanic glass, muscovite(Some volcanic glass may be pale brown) |
| Brown | Orthopyroxene |
| Green | Clinopyroxene, olivine |
| Red | Garnet |
| Yellow Green | Epidote |
| Dark Green to Black | Amphibole (some may be blue) |
| Green | Chlorite |
| Black (opaque) | Magnetite |
| Gold | Pyrite(opaque, with metallic luster) |
| Various (mat) | Lithic fragment |
Pointers for Comparing Colors
- The same mineral can occur in different colors, depending on its chemical composition. The general rule is the darker the color, the higher the iron/magnesium ratio (containing more iron).
- 2. As a general rule in color science, the more massive the sample, the more saturated its color appears (mass effect). In other words, even if a single grain of a mineral appears colorless, a color may be observable when you collect a larger quantity of the same mineral.
- 3. Consider color, like shape, as just one guide to identification. There are many exceptions!
