Obsidian and Porphyry
Definition
Definition
Obsidian is a naturally occurring volcanic glass formed as an extrusive igneous rock. It is produced when felsic lava extruded from a volcano cools rapidly with minimum crystal growth
Porphyry is a reddish-brown to purple igneous rock containing large phenocrysts of various minerals embedded in a fine-grained matrix
History
Origin
Ethiopia
Egypt
Discoverer
Obsius
Unknown
Etymology
From Latin obsidianus, misprint of Obsianus (lapis) (stone) of Obsius
From Old French porfire, from Italian porfiro and in some cases directly from Latin porphyrites
Class
Igneous Rocks
Igneous Rocks
Sub-Class
Durable Rock, Medium Hardness Rock
Durable Rock, Hard Rock
Family
Group
Volcanic
Plutonic
Other Categories
Opaque Rock
Fine Grained Rock, Opaque Rock
Texture
Texture
Glassy
Porphyritic
Color
Black, Blue, Brown, Green, Orange, Red, Tan, Yellow
Black, Brown, Colourless, Green, Grey, Red, Rust, White
Maintenance
Less
Less
Durability
Durable
Durable
Water Resistant
Yes
No
Scratch Resistant
Yes
Yes
Stain Resistant
No
Yes
Wind Resistant
No
No
Acid Resistant
No
Yes
Appearance
Shiny
Dull
Uses
Architecture
Interior Uses
Decorative Aggregates, Interior Decoration
Decorative Aggregates, Interior Decoration
Exterior Uses
Garden Decoration
Garden Decoration, Paving Stone
Other Architectural Uses
Not Yet Used
Curbing
Industry
Construction Industry
Arrowheads, Cutting Tool, Knives, Scrapers, Spear Points
Construction Aggregate
Medical Industry
Surgery
Not Yet Used
Antiquity Uses
Artifacts, Jewellery
Artifacts, Monuments, Sculpture
Other Uses
Commercial Uses
Creating Artwork, Mirror, Used in aquariums
Creating Artwork, Gemstone, Jewelry
Types
Types
Fireworks Obsidian, Mahogany, Sheen Obsidian, Snowflake obsidian and Velvet Peacock Obsidian
Rhomb Porphyry
Features
Blocks negativity, Helps to protect against depression
Generally rough to touch, Is one of the oldest rock, Surfaces are often shiny
Archaeological Significance
Monuments
Not Yet Used
Used
Famous Monuments
Not Applicable
Data Not Available
Sculpture
Not Yet Used
Used
Famous Sculptures
Not Applicable
Data Not Available
Pictographs
Used
Not Used
Petroglyphs
Used
Not Used
Figurines
Not Yet Used
Used
Fossils
Absent
Absent
Formation
Formation
When the lava is released from volcano, it undergoes a very rapid cooling which freezes the mechanisms of crystallization. The result is a volcanic glass with a uniform smooth texture.
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.
Composition
Mineral Content
Not Available
Biotite, Chert, Feldspar, Garnet, Graphite, Quartz, Silica
Compound Content
Aluminium Oxide, CaO, Iron(III) Oxide, FeO, Potassium Oxide, MgO, MnO, Sodium Oxide, Phosphorus Pentoxide, Silicon Dioxide, Titanium Dioxide
Aluminium Oxide, CaO, Iron(III) Oxide, Potassium Oxide, MgO, Sodium Oxide, Silicon Dioxide, Titanium Dioxide
Transformation
Metamorphism
Yes
Yes
Types of Metamorphism
Burial Metamorphism, Cataclastic Metamorphism, Contact Metamorphism
Burial Metamorphism, Cataclastic Metamorphism, Contact Metamorphism, Hydrothermal Metamorphism, Impact Metamorphism, Regional Metamorphism
Weathering
Yes
Yes
Types of Weathering
Biological Weathering, Chemical Weathering, Mechanical Weathering
Biological Weathering, Chemical Weathering, Not Registered
Erosion
Yes
Yes
Types of Erosion
Chemical Erosion, Coastal Erosion, Glacier Erosion
Chemical Erosion, Coastal Erosion, Glacier Erosion
Properties
Physical Properties
Hardness
5-5.5
6-7
Grain Size
Not Applicable
Fine Grained
Fracture
Conchoidal
Irregular
Streak
White
White
Porosity
Very Less Porous
Less Porous
Luster
Vitreous
Dull
Compressive Strength
0.15 N/mm2
33
Not Available
Cleavage
Non-Existent
Imperfect
Toughness
Not Available
1.7
Specific Gravity
2.6-2.7
2.5-4
Transparency
Translucent
Translucent to Opaque
Density
2.6 g/cm3
2.5-2.52 g/cm3
Thermal Properties
Specific Heat Capacity
0.92 kJ/Kg K
10
Not Available
Resistance
Heat Resistant, Impact Resistant
Heat Resistant, Impact Resistant
Reserves
Deposits in Eastern Continents
Asia
Afghanistan, Indonesia, Japan, Russia
China, Kazakhstan, South Korea, Thailand, Turkey, Vietnam
Africa
Kenya
Egypt, Ethiopia, Ghana, South Africa
Europe
Greece, Hungary, Iceland, Italy, Turkey
Finland, France, Germany, Great Britain, Hungary, Iceland, Ireland, Italy, Netherlands, Norway, Romania, Sweden, Switzerland
Others
Not Yet Found
Greenland
Deposits in Western Continents
North America
Canada, Mexico, USA
Canada, Cuba, Jamaica, USA
South America
Argentina, Chile, Ecuador, Peru
Bolivia, Brazil, Colombia, Ecuador, Paraguay
Deposits in Oceania Continent
Australia
New Zealand
New South Wales, New Zealand, Western Australia
All about Obsidian and Porphyry Properties
Know all about Obsidian and Porphyry properties here. All properties of rocks are important as they define the type of rock and its application. Obsidian and Porphyry belong to Igneous Rocks.Texture of Obsidian is Glassy whereas that of Porphyry is Porphyritic. Obsidian appears Shiny and Porphyry appears Dull. The luster of Obsidian is vitreous while that of Porphyry is dull. Obsidian is available in black, blue, brown, green, orange, red, tan, yellow colors whereas Porphyry is available in black, brown, colourless, green, grey, red, rust, white colors. The commercial uses of Obsidian are creating artwork, mirror, used in aquariums and that of Porphyry are creating artwork, gemstone, jewelry.
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