Definition
Porphyry is a reddish-brown to purple igneous rock containing large phenocrysts of various minerals embedded in a fine-grained matrix
Arkose is a sedimentary rock, specifically a type of sandstone containing at least 25% feldspar
History
Origin
Egypt
France
Discoverer
Unknown
Alexandre Brongniart
Etymology
From Old French porfire, from Italian porfiro and in some cases directly from Latin porphyrites
From Auvergne region of France used by a French geologist Alexandre Brongniart in 1826 who applied this term to some feldspathic sandstones
Class
Igneous Rocks
Sedimentary Rocks
Sub-Class
Durable Rock, Hard Rock
Durable Rock, Hard Rock
Family
Group
Plutonic
-
Other Categories
Fine Grained Rock, Opaque Rock
Coarse Grained Rock, Opaque Rock