Definition
Porphyry is a reddish-brown to purple igneous rock containing large phenocrysts of various minerals embedded in a fine-grained matrix
Gossan is intensely oxidized, weathered or decomposed rock, usually the upper and exposed part of an ore deposit or mineral vein.
Discoverer
Unknown
Cornish Gossen
Etymology
From Old French porfire, from Italian porfiro and in some cases directly from Latin porphyrites
From Cornish gossen from gos, blood from Old Cornish guit
Class
Igneous Rocks
Metamorphic Rocks
Sub-Class
Durable Rock, Hard Rock
Durable Rock, Medium Hardness Rock
Other Categories
Fine Grained Rock, Opaque Rock
Fine Grained Rock, Medium Grained Rock, Opaque Rock
Texture
Porphyritic
Rough, Sandy
Color
Black, Brown, Green, Grey, Red, Rust, White
Brown, Brown- Black, Gold, Green, Rust
Durability
Durable
Durable
Scratch Resistant
Yes
Yes
Appearance
Dull
Dull and Banded
Interior Uses
Decorative Aggregates, Interior Decoration
Countertops, Decorative Aggregates, Interior Decoration
Exterior Uses
Garden Decoration, Paving Stone
As Building Stone, As Facing Stone, Paving Stone, Garden Decoration, Office Buildings
Other Architectural Uses
Curbing
Curbing
Construction Industry
Construction Aggregate
As Dimension Stone, Cement Manufacture, Construction Aggregate, for Road Aggregate
Antiquity Uses
Artifacts, Monuments, Sculpture
Artifacts
Commercial Uses
Creating Artwork, Gemstone, Jewelry
Cemetery Markers, Commemorative Tablets, Gemstone
Types
Rhomb Porphyry
Translocated gossan and Leakage gossan
Features
Generally rough to touch, Is one of the oldest rock, Surfaces are often shiny
Clasts are smooth to touch, Easily splits into thin plates
Archaeological Significance
Formation
Porphyry is formed in two stages: the magma cools slowly deep within the crust or the magma is cools rapidly as it erupts from a volcano, creating small grains that are usually invisible to naked eye.
Earth movements can cause rocks to be either deeply buried or squeezed and hence the rocks are heated and put under great pressure.
Mineral Content
Biotite, Chert, Feldspar, Garnet, Graphite, Quartz, Silica
Apatite, Augite, Biotite, Bronzite, Calcite, Chert, Epidote, Feldspar, Hornblende, Micas, Plagioclase, Pyroxene, Quartz, Sulfides, Zircon
Compound Content
Aluminium Oxide, CaO, Iron(III) Oxide, Potassium Oxide, MgO, Sodium Oxide, Silicon Dioxide, Titanium Dioxide
Aluminium Oxide, CaO, Fe, FeO, Silicon Dioxide, Sulphur
Types of Metamorphism
Burial Metamorphism, Cataclastic Metamorphism, Contact Metamorphism, Hydrothermal Metamorphism, Impact Metamorphism, Regional Metamorphism
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Types of Weathering
Biological Weathering, Chemical Weathering
-
Types of Erosion
Chemical Erosion, Coastal Erosion, Glacier Erosion
Chemical Erosion, Sea Erosion, Wind Erosion
Grain Size
Fine Grained
Fine to Medium Grained
Fracture
Irregular
Conchoidal
Streak
White
White to Grey
Porosity
Less Porous
Highly Porous
Specific Gravity
2.5-4
2.0
Transparency
Translucent to Opaque
Opaque
Density
2.5-2.52 g/cm3
-9999 g/cm3
Resistance
Heat Resistant, Impact Resistant
Heat Resistant, Impact Resistant, Pressure Resistant
Deposits in Eastern Continents
Asia
China, Kazakhstan, South Korea, Thailand, Turkey, Vietnam
China, India, Indonesia, Russia, Singapore, South Korea
Africa
Egypt, Ethiopia, Ghana, South Africa
Cape Verde, Ethiopia, Ghana, South Africa, Western Africa
Europe
Finland, France, Germany, Great Britain, Hungary, Iceland, Ireland, Italy, Netherlands, Norway, Romania, Sweden, Switzerland
Albania, France, Germany, Great Britain, United Kingdom
Deposits in Western Continents
North America
Canada, Cuba, Jamaica, USA
Canada, USA
South America
Bolivia, Brazil, Colombia, Ecuador, Paraguay
Brazil, Colombia, Ecuador
Deposits in Oceania Continent
Australia
New South Wales, New Zealand, Western Australia
New South Wales, South Australia, Western Australia