Porphyry

Any igneous rock with large crystals floating in a fine-grained background.

Porphyry specimen — Photo: James St. John, CC BY 2.0, via Wikimedia Commons

How to identify porphyry

Distinct larger crystals scattered through a fine matrix.
Often purple, red or green.
Takes a high polish.

Often confused with

Andesite
Andesite is a porphyritic rock too, but gray and duller.
Compare side by side
Granite
Granite's grains are all coarse.
Compare side by side

Where it's found

Eastern Desert, Egypt
Älvdalen, Sweden
Saxony, Germany

Uses

Ornamental stone; 'porphyry' copper deposits are named after it.

Rock tumbling

Great for tumbling.

Did you know?

Purple Egyptian porphyry was reserved for Roman emperors.

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