In geology, sedimentary particles with diameters between 0.0625 (1/16)mm and 2mm are defined as sand. In ordinary speech, people often talk about coarser particles as sand as well, but in geological terms, these are granule.
Find a sample that makes you think, “This is pretty fine, isn’t it?” and you should be right on target. But don’t worry about particles that might be too fine. If you can rub them between your fingers and feel a bit of graininess, you should be OK.
In our fieldwork, we will collect two kinds of sand samples.The first is a bulk sample, with which to determine the overall mineral content of the sand. This can simply be shoveled into a specimen bag.
The second sample is used to concentrate the heavy minerals that are present in the sand. We will concentrate the heavy minerals because, in general, more information can be gleaned from heavy minerals like pyroxene, amphibole or zircon than from light minerals like quartz and feldspars.
How to Collect a Bulk Sample (to assess overall mineral content)
- Use a trowel to scoop up the sand.
- Strain it through a 2mm sieve (that’s about as fine as a kitchen colander) to remove roots, leaves, pebbles, and so on.
- Now, simply place your sample in a sample bag!
To concentrate and collect heavy minerals in the field, we use a method called panning, which utilizes the differences in the density of various minerals. A bowl or pan containing sand is rotated underwater, so that the relatively light minerals are expelled by centrifugal force, while the heavy minerals remain at the bottom for easy collection.How to Isolate Heavy Minerals: Panning for Black Sand
- Place one trowel full of sand in a bowl or pan.
- Hold the bowl at an angle just beneath the surface of the water, and swirl. Hint: For best results, the center of the bowl should remain under water, while the rim breaks the surface with each rotation.
- Continue until only about 1% of the original sand’s volume remains in the bowl.
- If the remaining sand is blackish, you’ve successfully panned for heavy sand!
