In the making of a pencil we have many different ingredients to consider, but the first of these we all know is the mainstay of the “lead” used in the item. This is not actually lead, but a graphite mix. I will cover other ingredients (such as the clay) in later posts.
The properties of graphite are listed below.
|Hardness||Associated Minerals||Streak||Colour||characteristics||Luster||Field Indicators|
|1 - 2||quartz |
|black gray to brown/ gray||black, silver||thin flakes are flexible but inelastic, mineral can leave black marks on hands and paper, weakly conducts electricity||metallic to dull||softness, luster, density and streak.|
For our exercise, the quality of the graphite is not so important. It is a common mineral, but one that is not found in quantity as a good pure source. This does not stop us finding it, but can make processing more difficult. For instance, graphite can be found in quartz. This is not uncommon, but quartz is an extremely hard mineral and mining graphite from a quartz deposit would be extremely hard work.
Lucky for us, graphite floats in water. So even if we have a deposit in another material (and we hope not one as hard as quartz) we can pound the mix into a powder and the graphite will float on water (were most other materials will sink).
But where do we find it?
If we are seeking a graphite deposit, we need to start looking for large deposits of felspar, mica, quartz, pyroxene, rutile, pyrites, and apatite. These minerals are commonly found with graphite. For our pencil we do not care to much about the quality and amorphous graphite will suffice. This is found in shale, slate, sandstone, quartz and limestone based rock formations.
I have included a number of images of graphite from http://minerals.net to aid in the determination of a piece of graphite. Graphite is grey to black in tone. Most of the time it has a shiny metal gloss and will smudge easily. If it is graphite, it should feel a little greasy to the touch and is in fact used as a dry lubricant. Molybdenite looks similar to Graphite but is heavier. The easy test is that this does not smudge as Graphite does.
Furthermore, graphite will make a mark on paper. In determining whether a rock happens to be graphite, start with a dark grey to black rock you have found in a limestone or shale area (and others as noted above) . Try and scratch it with your fingernail. Graphite is soft and will scratch easily.
For those of use who are close to a limestone cliff it is not too difficult to find graphite. It takes time and you need to mine into the rock, but at least limestone is nowhere near as hard as quartz.
With a good hammer and pick (which we have to make another time) we should be able to find a suitable quantity of graphite for one pencil in only 8 cubic meters of mined limestone. The main reason for this (even though we have more than enough for a single pencil is to account for the chance of finding a suitable deposit as well as having a large enough deposit to actually process).
The rate at which one mines will vary based on the strength of the person, the tools and the difficulty posed in the ground itself. In my case, I am a large 6’ male with good upper body strength. I needed to repair the picks at the end of this exercise but did complete 12 cubic meters of excavation. The blisters account for the exercise and it is not one I plan again.
This is basically a pit 2 meters in each direction. This was a 12 day exercise (and replaced going to gym and boot camp for a couple weeks of vacation). I cannot say I am far from the best miner but I am am also far from the worst. The main part to remember is that we are trying to find graphite deposits and as such the rock needs to be pounded rather finely.
Once we have sorted the deposits with some graphite (or at least a black substance in the limestone) we can pound and grind it to a powder. This is cast into water and left to settle for a few nights. The graphite will remain on the top floating as a the limestone sinks.
So, for two (2) weeks work and a total of 124.5 hours effort I was able to gain 328grams of low grade fine graphite powder. As a pencil generally contains between 1.001 - 1.067 gram of graphite we have a sufficient amount of graphite for just under 300 pencils in 124.5 hours of work. So far, in just extracting one raw material (without accounting for the wear on the tools we had to make) we have spent far more than we could have through trade.
In our exercise we will not measure cost and value in money. We will do this in time. This process will cover the finding, the extraction and even the tool making. In this, we are lucky to assume the knowledge is all available (as it is for us in the age of simple access to information). Just think how difficult and more time consuming this would have been if it was done using a library.
We also have the luxury of having food and shelter. Imagine if you also had to make and maintain a shelter and find food at the same time you have been looking for a suitable deposit of rocks.
I was lucky in this. I had a property where I could do this excavation with only a 1.2 km walk each morning whilst carrying 24-30 kg of tools. Not all areas are in metamorphic deposits and this would have been more difficult if I needed to walk further afield or to have mined in quartz.
Graphite time measurement – 0.415 hours per pencil
We will continue to investigate another part of the process next time. Just remember how amazingly complex a modern economy really is each time you look at a pencil and try to think what it takes to make a computer.
- Chesterman, Charles W. (1997) National Audubon Society Field Guide to North American Rocks and Minerals. Chanticleer Press, New York.
- Klein, Cornelis & Hurlbut, Cornelius (1993) Manual of Mineralogy. John Wiley & Sons, New York.