Two Large Stones Appear to Be the Same: One is attracted to magnets, the other isn't!

[dtinhb]

Hey all,

I have been stalking these posts for a few days and figured I would reach out and join the conversation. Recently, after a cross country trip I came home with quite a haul. Knowing nothing of rocks, I mostly brought home what intrigued me. Today I was going over my rock pile with a strong magnet (2" x 2") and I came across several rocks that the magnet stuck to. However, the one with the strongest attraction would have been the one that I would have said was least likely to have a magnetic reaction. (The rock is wet in the 1st picture, in the second its not) The really interesting thing is that another stone, that largely resembles this one, has zero magnetic reaction. The two in the third picture also resemble the larger two stones, but are about 10% of their size. The fourth picture is another rock, which had a strong attraction (though less than the first rock) to the magnet, but is not as dense. Any thoughts would be appreciated.

 

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[Eu_citzen]

Magnetism as strong as this is often due to small inclusions of magnetite, the more magnetite, the stronger the magnet is attracted to the rock.

Mafic rocks, such as gabbro, have a larger tendency to have magnetic minerals. But it's a rule of thumb and not always true.
In this case you have a (magnetic) mafic rock, perhaps even metamorphosed meaning in this case altered by heat or hot water-solutions.

Looking similar does not always mean they are the same rock.

 

[omurcelik]

i think this rock may be chromite...