🔎 UNIDENTIFIED Igneous rocks washed into a creek in north Texas.

[LanceHall]

I need help with identifying imported igneous rocks washed into a creek in Denton County, Texas. They are not native is all I know. I'm good with fossils but still new with rock types. I took these home for a rock garden they have so much character.

Are these Phorphry and/or Rhyolite?

 

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[HeavyMetalThunder]

I need help with identifying imported igneous rocks washed into a creek in north Texas. They are not native is all I know. I'm good with fossils but still new with rock types. I took these home for a rock garden they have so much character.

Are these Phorphry and/or Rhyolite?

porphyry's not a specific rock type, it's a term for for the texture (coarse and fine grains) for a broad range of rocks.

your brown reddish rocks are unmistakably Rhyolite ...

your dark grey/ black rocks, very likely Basalt less likely Andesite...better picture and a fresh (face) chip would tell a lot...small yellow to dark green crystals (Olivine) present would positive I.D. it as Basalt.

 

[LanceHall]

Awesome, thank you!

 

[LanceHall]

I found there is a layer in west Texas called the "Thunderbird" rhyolite of Precambrian age. The purple-ish rocks match very well with the picture below from a geology website. I think we have the source locality for the rocks I collected.

 

[HeavyMetalThunder]

yup, I re scrutinized your pics the gray/black rocks are rhyolite too... even with bad pictures, they've got that slightly glassy look from a high silica content...

very likely sourced from El Paso, southern New Mexico area as that has both color types.