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Identity HelpWhy is this chalcopyrite so magnetic? what is it?

4th Nov 2019 18:59 UTCSusan Wakeman

My purchased sample of chalcopyrite is very magnetic. Or is it a mix with other minerals?

4th Nov 2019 19:16 UTCAntonio Nazario

Chalcopyrite's chemical formula is CuFeS2. Both copper and iron can attract a magnet.

5th Nov 2019 01:31 UTCKyle Bayliff

I encourage you to test that statement... Pure elemental copper is diamagnetic. It will noticeably repel a strong enough magnet, but it will not attract.  And much like NaCl has both chlorine and sodium in it, but is neither a toxic gas nor does it combust spontaneously in water, compounds containing elements we think of as magnetic may not be magnetic themselves. For example hematite contains iron and is actually an antiferromagnet (it has 0 magnetic moment as long as the applied field is not too high).

Conversely, there's a very rare class of magnets called itinerant magnets that show magnetic order despite being composed solely of constituents with closed electron shells (e.g. Sc and In are both essentially non-magnetic, but Sc3.1In is a weak ferromagnet). Itinerant magnetism is even less well understood than conventional magnetism, but it is thought to result from the correlated wave behaviour of conduction electrons acting as the magnetic moment carriers.

5th Nov 2019 11:31 UTCThomas Lühr Expert

A more simple example: Stainless steel is an alloy from iron with a few other components like Cr, Ni, Mo. And it is ... NON-magnetic! 

4th Nov 2019 19:42 UTCKevin Conroy Expert

The non-iridescent part of your specimen looks dark, so you may have bornite instead of chalcopyrite.   Same elements as chalcopyrite (except Cu5FeS4), so Antonio's statment still applies.

4th Nov 2019 19:48 UTCAlfredo Petrov Manager

Likely it is from a skarn and mixed with magnetite or pyrrhotite, both of which are very much more magnetic than chalcopyrite or bornite.

4th Nov 2019 20:01 UTCGeorg Graf

Hi Susan,

Chalcopyrite is not magnetic! There must be an impurity in your specimen, e. g. Pyrrhotite.

Kind regards, Georg

4th Nov 2019 21:03 UTCMichael Hatskel

Hi Susan,
What kind of magnet are you using?

4th Nov 2019 21:50 UTCJolyon Ralph Founder

I think your magnet is very magnetic :) 

4th Nov 2019 23:02 UTCSusan Robinson

Why not do a specific gravity test on the chalcopyrite ball to make sure it is chalcopyrite?

4th Nov 2019 23:25 UTCTom Tucker

I assumed the ball is his magnet.   I've never heard of magnetic chalcopyrite either.  

4th Nov 2019 23:33 UTCAlfredo Petrov Manager

Well, there‘s cubanite, which is magnetic and looks like chalcopyrite in massive form, but it‘s not very common.

5th Nov 2019 03:21 UTCHarold Moritz Expert

No other common mineral besides magnetite will hold itself to a magnet like your piece is. So there is magnetite in there with the chalcopyrite (I see plenty of gray area on the left side), or it is magnetite coated with an iridescent film to make it a more attractive buy, like some quartz crystals have been.

5th Nov 2019 11:23 UTCThomas Lühr Expert

No other common mineral besides magnetite will hold itself to a magnet like your piece is.
There is still pyrrhotite that will also strongly attract by a magnet to hold itself on it. And it looks similar to chalcopyrite - freshly broken bronce colored and later brownish tarnished. Furthermore, cubanite may a possible candidate, like Alfredo wrote. It tarnishes also blue, but i can not say how strong the magnetism is.

5th Nov 2019 09:36 UTCJohan Kjellman Expert

try magnetizing a finer instrument (needle) and see what part of the specimen attracts it

5th Nov 2019 13:04 UTCA. Mathauser

Chalcopyrite occurs with other copper minerals - and with magnetite - both massive or in crystals - of many kinds (example: Mineral Hill, Maryland), and even microscopic crystals of magnetite have a tendency to attract magnet.

5th Nov 2019 17:33 UTCDonald B Peck Expert


I would apply Occam's Razor here . . . and until proven otherwise assume there is magnetite in your specimen.  The alternatives are generally weakly magnetic . . .not strong enough to support the weight of the specimen.  Unless that sphere is an unusual magnet.  What can you tell us about it?


5th Nov 2019 18:57 UTCThomas Lühr Expert

I have to disagree. Magnetite is NOT the only mineral with the property to hold the own wight, as the little experiment in the attached video shows.
A usual ceramic magnet with normal strength is easily able to pick up and hold a piece of pyrrhotite (min ID YFM-2JR), even with a lot of adhering non-magnetic matrix.

6th Nov 2019 14:39 UTCHarold Moritz Expert

Interesting. Well, I've collected pyrrhotite many, many times and it never does that, if anything it can get a suspended magnet to deflect slightly when held nearby.  If that is pyrrhotite, then suggest explore this as a subject for another thread. In any case, I have to agree with Dana below that the piece in question is most likely a mix of magnetite (which from anywhere will stick to a magnet every time) and chalcopyrite.

6th Nov 2019 15:40 UTCThomas Lühr Expert

Pyrrhotite exists in many polytypes, if i remember right, ther is even one that is not magnetic at all. So it is likely that some exist with weaker magnetism. It has been already discussed some time ago in an other thread (that i can't find right now).
All stuff that i had in hands (from Harz Mts. / Germany) show the same strong magnetism.

6th Nov 2019 15:47 UTCAlfredo Petrov Manager

Harold, I agree with Thomas that pyrrhotite magnetism can vary from strong to none. There are several polytypes, with variable deficiencies in Fe. Counterintuitively, the more the Fe deficiency the stronger the magnetism, and the variety with no Fe deficiency at all, troilite, FeS, is not magnetic at all (in the sense of being noticeably attracted to a hand magnet).

8th Nov 2019 14:02 UTCHarold Moritz Expert

Yup, I am aware of the polytypes, didnt realize that it got so magnetic at one extreme. But magnetite certainly a much more "reliable" attractant. Much of the pyrrhotite around here (NE USA) breaks down (like or worse than "pyrite disease") and can be identified by its awful irony sulfate smell (and sometimes taste just from the evaporating water) when wet and typically weak magnetism. In fact it is wrecking home foundations where it was unknowingly present in crushed stone used in the concrete. I'd systematically check the magnetism of the ones in my collection except that they are most gone to dust!

6th Nov 2019 14:18 UTCDana Slaughter

I would like to echo Alfredo's point that it is likely magnetite. There is a wholesaler in Tucson that has been marketing chalcopyrite and magnetite from NM. He has it out on his property to weather (with a little help) to produce the colorful "peacock ore" look and I have purchased a few larger pieces as the locality might be of interest to ore collectors. This may not be from this particular mine and, as mentioned, skarn zones, frequently host magnetite associated with copper ores.

10th Nov 2019 21:43 UTCMatthew Droppleman

That must be a strong magnet! My piece isn’t magnetic but my metal detector does beep when I’m near it... Any relation?

10th Nov 2019 21:57 UTCThomas Lühr Expert

Matthew, the metal detector is reacting zo the electric conductivity, not to the magnetiesm. 
As for the magnetism: see Alfredo's answer above. Pyrrhotite isn't like pyrrhotite.
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