enter image description here

There is a metallic shine on it that does not clearly show in the photo

This cube weighs 458g

Dimensions: 55mm H x 45mm W x 39mm D

Is this a Pyrite cube?

Thank you

  • $\begingroup$ It could be block of pure iron. How can we confirm if this is pyrite just from the photo? Have you conducted any physical/chemical test? $\endgroup$ Commented Apr 13, 2023 at 7:47
  • 1
    $\begingroup$ Working out the density would probably be simplest. $\endgroup$
    – porphyrin
    Commented Apr 13, 2023 at 8:19
  • 2
    $\begingroup$ It isn't even clear in the photo what colour it is. Pyrite is brassy/golden in colour. Is this cube that colour? $\endgroup$
    – matt_black
    Commented Apr 13, 2023 at 8:48
  • $\begingroup$ @NilayGhosh the density is too low for iron and galena, which I also checked, but comes close for pyrite. See below for suggested additional tests. $\endgroup$ Commented Apr 13, 2023 at 12:12
  • $\begingroup$ Iron is out if it does not pass the magnet test, i.e., if a magnet is not attracted to the specimen. $\endgroup$
    – Ed V
    Commented Apr 13, 2023 at 14:50

1 Answer 1


Pyrite is a reasonably good guess. Calculating the density of the cube from the reported measurements gives 4.7 g/cm³, using the same number of significant digits as those reported in the length measurements (and assuming a geometrically perfect block). Assuming the length measurements are correct to within $\pm0.5$ mm the possible range of densities is 4.6-4.9 g/cm³. This overlaps he reported density of pyrite 4.8-5.0 g/cm³. You may also check the hardness (pyrite = 6-6.5 Mohs, from the source cited above) and streak (greenish-black, Ibid.); the latter is often a better color measure than the apparent surface color because it is less subjected to surface impurities. If you have access to a lab that does X-ray diffraction, then pyrite has a distinctive and well-recognized pattern and the test, unlike the others I mention, is completely nondestructive.

  • 1
    $\begingroup$ I agree with your guess. If I had the specimen, I would test with an ohmmeter (to eliminate metal alloy of some sort), do the streak test you suggested, rub a specimen face with white paper, and add a drop of vinegar to the rubbed off stuff on the paper. Any rotten egg smell would likely mean pyrite, since galena is ruled out by the density. $\endgroup$
    – Ed V
    Commented Apr 13, 2023 at 15:39

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