Sanding and Polishing Meteorites by Hand

I have never owned a powered lapidary polisher. I have always done all of my sanding and polishing by hand. I used to find it relaxing and I actually enjoyed the work of it. As I get older and my hands get weaker and shakier, I don’t enjoy it any more and the quality of my work suffered. I just don’t polish like I used to 10 or 15 years ago. I don’t think I have hand polished a meteorite slice since around 2015, give or take. So now if I offer a polished slice, somebody else polished it before I acquired it.

I am offering some unclassified and unpolished meteorite slices. These pieces would look a lot better if they were polished and they would actually increase in value, but not enough for me to try polishing them up for resale. They might be worth your time if you are keeping these pieces for your own collection (some would make nice pendants when polished). Bearing this in mind, I am going to make a brief and simple guide here to polishing your own meteorite slices by hand without using an expensive powered lapidary polisher. Without further ado, let’s go …

What you will need :

1) an unpolished meteorite slice or endcut that has a flat dull face and/or saw marks on it.

2) a selection of sandpaper in progressive grits from 200 up to about 1000 or 1200 grit. You should have several like : 200, 400, 600, 800, 1000, etc. Preferably a few sheets of each grit. Note, the highest grits can be hard to find. While the lower grits are common at your local big box store or home improvement store, you may have to visit an auto parts store to get the 1000+ grit. Those higher grits are sometimes used by people who do auto body and paint work.

3) a well-lit, sturdy, hard, flat surface to work on : a kitchen table, desk, or workbench.

4) optional “Jeweler’s Rouge” in cloth, powder, or paste form. (more on this below).

5) An old expendable soft cotton T-shirt, rag, or scrap cloth (for the final stage of polish).

Unpolished meteorite slices/endcuts are not all equal when it comes to sanding and polishing. Individual meteorites can vary in texture and hardness. One chondrite might be softer or harder than a similar-appearing chondrite. Also, you may notice more or deeper saw marks remaining on the slice, depending on the equipment used to cut it and the skills of the cutter. An amateur hand cutting on a small lapidary saw might leave behind more and deeper saw marks than a professional cutting the same meteorite on a $10k diamond wire saw rig. Keeping this in mind, some specimens will require more work to clean up than others. A light sanding might do the trick on a given slice, while another piece with deep saw gouges will require more elbow grease to make it pretty.

The pieces I offered last week and the ones I am offering this week were cut on a diamond wire saw, so they don’t have any deep saw marks. What they do have is a bunch of shallow grooves that are unsightly, but are relatively easy to remove with just a moderate sanding job. In addition, some meteorite types look better after polishing, but a few do not. Sometimes the polishing process will darken or muddy fine details like tiny chondrules. You generally can learn from experience which is which by looking at them. These pieces are the types that could benefit from a good polishing and would look a ton better afterwards. So, let’s get to work.

For the newbie – sandpaper grits are numbered from smallest and roughest to highest and smoothest. A 100 or 200 grit feels very rough when you run your fingers over it. This is the type of sandpaper used to remove deep gouges. With these wire-cut slices, you may not need a rough 200 to start. You might be able to start with a 400. A little trial and error is necessary here.

Ok, so you have your specimen, your sandpaper, a well-lit hard surface, and now you are ready to polish.

Place a sheet of the rough starting grit (200 or 400) on the table with the gritty side facing up. You can tape it or pin it in place, but you’ll probably end up holding it down with your offhand while you sand with the dominant hand.

Take the specimen in hand and put the flat face directly down on the sandpaper and press firmly. Now, while pressing firmly, move the specimen in circles around and around. Do not sand in straight lines because you aren’t sharpening a knife blade here. You want to get a good, smooth, consistent motion going in circles. Do this for a period of time (more trial and error!) and then stop. Blow off the loose grit from the table and the piece, wipe it with a cloth, and look at it. It should look smoother and most of the saw marks should be gone or very reduced. If not, then keep sanding. Once you feel like it has stopped improving and the piece isn’t looking any better, then stop and proceed to the next grit level.

Put aside your rough grit 200 piece (or toss it if it’s worn out) and put down the next finer grit paper. Repeat the above process of using firm circular motions to sand down the flat exposed face. By this time, all of the rough saw marks should be completely gone to the naked eye. Now you are just about done with the “sanding” part of the job and you are getting to the “polish” stage of this process.

You will also notice that each stage of the process is a little easier and shorter than the previous. Most of your elbow grease will take place in the rough 200 grit phase (or 100 grit if you have some pieces with deep gouges on them). By the time you finish the 400 grit stage, you are getting to the payoff part and you should start to notice some shine or glossiness – this is polish. Once you feel like the specimen isn’t improving any further, stop. Wipe off the loose grit and proceed to the next stage of 600 (or 800) grit.

None of this is exact science and you will learn by feel and look what to do and how long to do it at each stage. Maybe you start with 100 grit and stop at 800. Maybe you start at 400 and stop at 1200. Each stage doesn’t have to be an exact jump or doubling of grit size. You can skip 400 and go to 600. Or, maybe you go from 400 right to 1000. It depends on the material and how hard/soft it is. Some meteorites will take a higher polish than others. A softer and more friable meteorite may not take a high glossy polish. A hard and tough chondrite may take a high glassy polish that has a mirror-like finish. Even the weathering state of the specimen plays a role here. A fresher meteorite may polish differently than a weathered example of the same material.

Keep polishing in circular motions through each grit stage until you get to 1000 or 1200 grit. Higher grits exist but you don’t really need them for our purposes. We are not polishing a telescope mirror here, we are polishing a slice of rock, so no need to go crazy. Once you get to about 800 or 1000, you will have a very shiny and smooth slice where the surface features are more visible. The chondrules should (but not always) be more visible and the metal flecks will be shinier. The matrix material should be darker and that will make contrasting components like clasts and inclusions really “pop” when looked at.

You decide when you are finished. When it stops looking better, you are done. And what looks better is somewhat subjective, so each slice might have a slightly different feel and process before you deem it a done job.

Ok, we are done with sandpaper. What about that Jeweler’s Rouge? This stuff is available from lapidary supply vendors, some rock shops, and you might be able to find some at a jewelry store. The kind I like best comes in a cloth form. The “rouge” is a fine polishing grit (likely 2000 or higher) that feels very smooth to the touch. You may have noticed that higher grit sandpaper like 1000 or 1200 has a velvety feel to it, almost like suede or velvet. You can buy Jeweler’s Rouge cloth that has the grit embedded in it and is less messy to work with. Take a piece of rouge cloth and put it flat on the table like you did with the sandpaper and repeat the process of firm circular motions. This won’t take long. Just a few minutes of this and you may see a very glassy and glossy polish like a mirror. This step is optional, but can produce fine results. Note, rouge sometimes has color tint in it. Try to find a neutral color rouge so you don’t stain your specimen with a light red or green color. You want shine, not added artificial color.

If you don’t have Jeweler’s Rouge, you can use an old cotton T-shirt. Put it flat on the table and use circular firm motions just like you did during polishing. Now you should have a pretty polished meteorite slice that looks a lot better than when you first started. And, as an added bonus, you just increased it’s monetary value because a pretty polished slice will always sell for a little more than an unpolished example.