Unusual Rock - Mudstone Inclusion

[19.3]

Hi Folks,
Found this unusual rock with the 2300 at the beach, it did not howl as loud as iron or steel, but at a distance of about 200mm was a very clear hum. It was captive in a hollow in the bedrock and covered in sand.
The bedrock is Boonanghi as defined by the App Trilibite - see screenshot.
It's a very interesting rock with several different features.
Any suggestions?

 

[grubstake]

Are you sure that isn't just the totally corroded remains of a lump of old iron?

 

[19.3]

I don't think it is a rusty lump of iron. For one it does not appear flakey.
Also it appears to include a number of 'nodules' of black crystalline material which sparkles in the light. The nodules are covered in a thin 'rusty' crystalline crust which appears to have grown on the outside. These appear to have sections 'chipped' off exposing the black interior - probably due to tumbling by wave action in a hollow in the bedrock.
The rock does not have its own magnetism, but a magnet does stick to it.
Interestingly, given its size I would expect it to send the 2300 wild but while it is a strong signal, it is nowhere near as strong a signal as I would expect from a lump of rusty iron.

 

[mbasko]

IMO it's beach weathered iron/steel slag.