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I need help identifying this rock please. I found this around Louisiana a few weeks back. To me it looks like raw Platinum or an ore maybe. I’m not really good at this yet haha. It’s not magnetic at all, it’s weight is 3.7 grams, and it’s streak is too hard to get, as it only scratches the plate. So possibly even a meteorite? Idk  heh. Thanks you!!

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Could be a piece of slag. Where did you find it was it in the middle of nowheres or near a farm etc?

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  • 2 weeks later...

Slag (in geological terms) is the stony leftover material after ore has been smelted.  This sample looks too metallic and could be melted aluminum, tin, pewter or a type of metal alloy melted after a fire of some sort.  The holes in it are not common in meteorites. I think KAC is on the right track identifying it, something left over from a human cause like a furnace or maybe even a structure or trash dump fire.

Another good measurement to get for it is density, If you have a graduated cylinder or another way to estimate the volume, use it to find the volume (the easiest is to find the displacement of water in cc’s using a graduated cylinder) and divide the weight by volume, g/cc.  This will make it easier to identify the metal. Platinum is denser than gold, at 21.4 g/cc. vs. gold at 19.3 g/cc. You’ll feel  the difference when you’re holding it.

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......Do an "aqueous weighing test" ... to find out what this piece of metal has .. a specific gravity, then you can say something more about this material ..platinum has a very high specific weight ,,

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Unfortunately determing volume by simple displacement (e.g. graduated cylinder) in practice has too much uncertainty to be of much use.  "Aqueous weighing test" is also susceptible to considerable uncertainty (see below) if the scales used aren't sufficiently precise.  The weight of the piece is typically the easy part.  Measuring displacement is where the uncertainty usually enters at a significant level.  The rest of this post is more general, addressing the uncertainties that can occur when doing a water displacement specific gravity measurement to determine an unknown's true identity, using the initial post's sample to illustrate.

Let's take the piece shown as an example.  3.7 g weight (scale presumably has a least significant digit of 0.1 g).  Here are some examples of associated volumes for common pure metals, except steel which is an iron alloy (using data from GotAU's table) in milliliters (which is the same as cubic centimeters -- note that specific gravity is effectively g/ml with units left off).

Aluminum -- 1.36 ml

Steel -- 0.47 ml

Copper -- 0.41 ml

Silver -- 0.35 ml

Lead -- 0.33 ml

Gold -- 0.19 ml

The volumes (i.e. water displacement) measured by a scale with 0.1 g precision will be respectively 1.4 ml, 0.5 ml, 0.4 ml, 0.4 ml, 0.3 ml, 0.2 ml.

Each measurement will have an absolute uncertainty of 0.05 g (or ml) -- note this includes the reported 3.7 g weight ==> assuming the scale is properly calibrated, this is anywhere between 3.65g and 3.75 g.  Let's look at the extremes of specific gravity for using a scale with least significant digit 0.1 g for samples with each of the above compositions:

Aluminum: 2.5 --> 2.8

Steel:  6.6 --> 8.3

Copper:  8.1 --> 10.7

Silver:  8.1 --> 10.7

Lead:  10.4 --> 15.0

Gold:  14.6 --> 25.0  (OK, the highest elemental s.g. is Osmium at 22.59 so you can be confident it's not 25.0)

To clarify, an actual sample of each of these metals which weighed 3.7 (plus or minus 0.05) g and whose water displacement was measured on a scale with 0.1 g least significant weight (so volume is measured with an uncertainty of plus or minus 0.05 ml) could give a value of specific gravity anywhere in the ranges above.  For this choice of metals and a 3.7 g weight, the worst separation is copper vs. silver and there is overlap on all neighbors in the list except aluminum.  But of all metals (including alloys) known, this is a drop in the bucket of possibilities.  Most (at least common) metals fall between iron and lead, and thus this range is the most difficult to separate.  But even the high end, population including tungsten, gold, and platinum you really can't tell these metals apart with this low of precision scale (and this size of sample) with even lead having some possible overlap as seen above.  In this case you can get crude separation:  something like grouping of {aluminum, steel/copper, copper/silver, silver/lead, heavy} and that might eliminate a candidate such as platinum -- one of the OP's proposed metals.

Conclusion:  get a scale which reads to 0.01 g.  (And for much smaller samples, "fly poop" size, get one that reads 0.001 g.)  Better yet, sweet talk someone with an XRF gun (calibrated to the proper range of elements...) to perform an elemental analysis.

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