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Identity HelpPseudomorphose: What after what?

11th Sep 2019 21:53 BSTManuel Maia

03941650015682310504851.jpg
Opinions about this  sample are very welcome!
Loose "cube" self-collected on the margins of  Caniçada barrage (Nort of Portugal) in the late 90's
Dimensions: +/- 1 cm edge


11th Sep 2019 22:09 BSTRalph Bottrill Manager

It looks like a feldspar porphyry that has accidentally broken into a cubic shape due to natural jointing?

11th Sep 2019 22:59 BSTPaul Brandes Manager

What about a rhyolite porphyry?

12th Sep 2019 09:24 BSTRalph Bottrill Manager

Quite likely, but feldspar porphyry also allows for it potentially being a dacite etc.; you could check if the phenocrysts are Kspar, plag, quartz etc.
 
Mineral and/or Locality  
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