Volcanic Rocks?

[Kiros32]

I found a couple of "rocks" tonight (pictures soon) that hit on my detector. They weigh next to nothing and one reminds of of pumus. The other is very shiny and reminds me of shale because of it's flaky texture. Both are black. Any idea what these could be?

 

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[nebraskadad]

Do you have pics?

Could be oxidized iron pyrite..

 

[bakergeol]

Yep -basaltic rocks because of their high Fe content do ring off on a metal detector. If you see big holes probably scoria.

HH
George

 

[Rusted_Iron]

Coal cinders sometimes hit hard on a metal detector. They can be very lightweight and have a flaky, shiny appearance. Not sure that's what you've found, but it could be.

Some kinds of slag resemble pumice. Finding both these rocks together makes me think that's what you've got, a coal cinder and a piece of slag.