electric spark from magnet powder - what could have been the reason?

[S Claus]

Here's a question about an experience I had when I was about 10 years
old. A friend of mine had obtained from somewhere a matchbox full of
'magnet powder', in fact a magnet that had somehow been ground to very
small pieces. We were playing with this powder with our fingers and at
one point the powder gave up a noticeable electric spark. We tried to
replicate the spark again but no luck. I have afterwards been thinking
that perhaps it was caused by static electricity that had first
transferred from our hands to the powder. Perhaps this was the reason
why we could not replicate it (as we would have had to 'charge
ourselves' on a carpet or something first)?

Or is there any other possible cause for this type of a spark?

Thanks in advance