What is this rock and what created the strange pattern?

[Mollymolly]

Hi!

I signed up for this website just to ask this question. I found this rock somewhere along Southern California coast. Most likely Northern San Diego County as that’s where most of my rock collecting is done. I have never seen one like it. Any input would be greatly appreciated. I’m so curious about it!!

 

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[Kray Gelder]

My guess would be black tourmaline inclusions in microcrystalline quartz.

 

[Ponchosportal]

Either hornblende or tourmaline in quartz. MO it is not microcrystalline and likely hornblende.

 

[hvacker]

Magic Marker?? Kidding!

 

[Kray Gelder]

Either hornblende or tourmaline in quartz. MO it is not microcrystalline and likely hornblende.

Yup. After checking out some images, a more likely guess.

 

[Eu_citzen]

Could also be amphibole, but tourmaline or hornblende are also perfectly good candidates.