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(Newbie) Identification Help - Magnetic rock found in yard in SF Bay Area


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Hi, I'm a new forum member and a newbie when it comes to minerals, so I'll apologize in advance if I don't provide sufficient information or use incorrect terminology.  I found this stone in my yard in Portola Valley, CA. I'm pretty sure it did not end up there naturally since I've never seen any rocks like this in the San Francisco Bay Area.  It stood out to me which is why I grabbed it. 

  • The rock is about 7" long
  • It appears to be a dark, grayish green in color
  • If you look closely it appears somewhat composite kind of like a granite
  • It has a "gemmy" quality to it in that it is shiny and smoothly worn
  • It is magnetic, which is what made it weird enough for me to post

I've done the usual internet searches filtering down by magnetic minerals, but I'm not good enough at this to feel very confident based on internet pictures. Any ideas are greatly appreciated. I'm happy to get more information if there is something that would help in the identification or if I didn't take good pictures.








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I've been doing some more internet searching since I posted this. I'm wondering if the rock might be serpentinite. Serpentine rock & soil is very common in my area (although usually more green and less gemmy than this stone). Evidently serpentinite can contain magnetite, which would explain why it is pretty strongly magnetic.  This photo (admittedly of a mineral from the Italian alps) looks remarkably like my rock:





Curious to get the perspective from experienced mineralogists.  I'm worried I am "wishing an identification" and cherry picking one picture that kind of looks like mine :-)

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