|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
What can this material be? |
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
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
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
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
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.
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
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!
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.
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.
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.
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
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
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:
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