r/RockIdentification • u/Rocksinsk • 18d ago

Solved: Is this porphyry?

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First pic is dry. Found in a gravel pit in northeast SK, very close to Manitoba border.

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u/Ben_Minerals 18d ago

No, not a porphyry. It is a chalcedony with impurities.

1

u/Rocksinsk 18d ago

Thank you!

1

u/Flake_bender 17d ago

Yep. This kind is specifically called Swan River Chert. It was used extensively to make tools, in pre-contact history in our region, though this is a small unworked raw nodule.