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Hi, I'm helping my young neighbor to determine what his "small fist" item is. It looks like a dark rock with a crusting on it - very hard, can't be broken open with a sledge hammer. Machine shop grinding of one edge took an extremely long time, again, very hard. very dense and heavy, very heavy, perhaps heavier than lead. Please give us some advice. What can this material be?
Question Date: 2015-09-07
Answer 1:

I would guess that it's not a crystal, because even a very hard crystal would break when hit with a hammer (a blow from a hammer will shatter a diamond).

Step #1. Put the small fist in a measuring cup. Next, fill up the cup with water, up to the top mark (use the metric scale on the cup). Now, remove the small fist from the cup, and see how much lower the water is from that top mark. This will give you the VOLUME (in milliliters, if you used the metric side of the cup) of the small fist.

Step #2. Weigh the small fist on a scale. Calculate the MASS in grams (one pound of weight should equate to 454 grams). If your scale already reads kilograms, you can skip this calculation.

Step #3. Divide the MASS by the VOLUME. This will give you the density. If you've done it right, then this density will be in grams per milliliter.

Step #4. Figure out what materials it might be based on its density. If you still aren't sure, you can email us once you have the density. Some numbers to use for reference:

Material ... Density
Water.........1 g/mL
Quartz.......2.6 g/mL
Hematite...5.6 g/mL
Iron............7.9 g/mL
Lead..........11.3 g/mL
Uranium.....19.1 g/mL
Gold...........19.3 g/mL

If its density is less than 5 g/mL, then it's probably a rock. If it's more, then it's probably a metal. If you can send photos of it, that might help as well.

Answer 2:

This is a very difficult question to answer without being able to see and feel the rock itself. To help you try and decide what type of rock you have, here is some background information that might help you do a little more research.

There are three main categories of rocks, sedimentary, igneous (volcanic), and metamorphic rocks. Each of these types of rocks is defined by different properties. A few of these properties that can help distinguish a rock type are its color, density, hardness, the way it fractures, minerals, luster, etc. You might want to ask yourself if the rock you have contains minerals. Different types of minerals define different types of rocks. If minerals are present you most likely have an igneous or metamorphic rock type.

Below are two links to flow charts that can help in distinguishing which type of rock you may have (i.e. sedimentary, igneous, or metamorphic). From there, it may be easier to use your resources and come up with a name for your rock!

GeoArcheo I
GeoArcheo II

Answer 3:

Unfortunately, it can be extremely difficult to identify a rock without seeing it up close (sometimes very, very close with a microscope or hand lens), and sometimes even then it isn’t easy. Based upon what you describe, it sounds like the rock might be a piece of iron, perhaps even a piece of iron or steel slag, both by-products of iron making. Steel slag often has a dusty black “crust” on the outside, and would be very hard and dense. They also often look very much like rocks you might find in the natural environment, and many people mistake pieces of slag for meteorites. It might be worth looking up pictures of iron and steel slag to see if they match your neighbor’s item.

Answer 4:

You have already tried some great techniques to determine what your material is! Scientists use very similar techniques to identify a mystery material. It is very difficult to tell you exactly what you're looking at without seeing it in front of me, but there are some other things you can try to help you identify it. For instance, you can rule out it being a meteorite if it's not magnetic. You can rule out it being a salt if it doesn't taste salty. Some other techniques we use are melting point (this is often a very good way to tell materials apart because each material has a distinct temperature at which it melts). To determine some rock types, we even put a little acid on it -- if it fizzes than it is part of the limestone rock family.

The last thing that helps to tell what it is, is knowing where you found it. Some rocks are only found in very specific areas, just as some plants only grow next to water or only in the desert. Maybe you can try a couple of these to help narrow down your search.

Answer 5:

More observations are needed for an educated guess of the identity of your "item". Careful observations are key to discovery. As a geologist, there are several tests you can use to help narrow down the identity of an item.

Here are some key questions and/or methods that can help. Take careful notes and be very specific when answering these questions. The more precise/specific you answer these questions, the more likely you'll discover the identity of the material.

1 What color is the item?
2 What color is the "crust?"
3 Do you see any pits/holes in the item? (How big are the holes?/What shape are they?)
4 What patterns/shapes do you see on the face (i.e., the "one edge") you ground with the grinder? (How big are the shapes? Color? etc.)
5 What patterns/shapes do you see on the outside surface? (How big are they? Color? etc.)
6 Scratch the item with a nail to see if the nail scratches the item.
7 Scratch the item on some glass to see if it leaves a scratch etched in the glass.
8 What color does the item leave when you scratch it on a piece of white paper?

For questions 3, 4, and 5 you could use a magnifying glass to get a closer, careful look.

From your description, the item may be a rock, but it could also be a man-made object. I don't have a guess. However, if you answer questions 1-8 and then give your answers to a geologist, your geologist friend can help you identify the item more effectively.

Answer 6:

You are on the right track, focusing on hardness and density. Here’s a list of things you may not have tried or considered:

1 – Is the crust a different material with different properties? Is it only on the outside or incorporated inside? If it’s only on the outside, the rock most likely contains metals that have oxidized on exposure to air and water. Can the crust be dissolved with vinegar? How does the metal respond to vinegar?

2 – Is it inherently magnetic or respond to magnets? Test it out by bringing it close to some paperclips and a refrigerator magnet. Very few rocks are inherently magnetic and metals that respond to magnets most commonly contain iron.

3 - Calculate its density (weight/volume) so that you can directly compare it with rocks’ and metals’ properties online to eliminate many possible candidates.

4 - Try to quantify how hard it is by seeing if it can scratch or be scratched by different materials. (Be careful of your hands as you scratch and be sure to use material you don’t mind damaging.) That can give you a hardness range that will also eliminate possible candidates. This website has a description of what materials to try: here

Identifying rocks takes patience and ingenuity, as you’ve already discovered, and attracts many hobbyists. A similar set of questions on this website may also help you:

click here

Good luck!

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