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
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
Other Categories
Opaque Rock
Fine Grained Rock, Opaque Rock
Texture
Glassy
Porphyritic
Color
Black, Blue, Brown, Green, Orange, Red, Tan, Yellow
Black, Brown, Green, Grey, Red, Rust, White
Durability
Durable
Durable
Scratch Resistant
Yes
Yes
Interior Uses
Decorative Aggregates, Interior Decoration
Decorative Aggregates, Interior Decoration
Exterior Uses
Garden Decoration
Garden Decoration, Paving Stone
Other Architectural Uses
-
Curbing
Construction Industry
Arrowheads, Cutting Tool, Knives, Scrapers, Spear Points
Construction Aggregate
Medical Industry
Surgery
-
Antiquity Uses
Artifacts, Jewellery
Artifacts, Monuments, Sculpture
Commercial Uses
Creating Artwork, Mirror, Used in aquariums
Creating Artwork, Gemstone, Jewelry
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
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.
Mineral Content
-
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
Types of Metamorphism
Burial Metamorphism, Cataclastic Metamorphism, Contact Metamorphism
Burial Metamorphism, Cataclastic Metamorphism, Contact Metamorphism, Hydrothermal Metamorphism, Impact Metamorphism, Regional Metamorphism
Types of Weathering
Biological Weathering, Chemical Weathering, Mechanical Weathering
Biological Weathering, Chemical Weathering
Types of Erosion
Chemical Erosion, Coastal Erosion, Glacier Erosion
Chemical Erosion, Coastal Erosion, Glacier Erosion
Grain Size
-
Fine Grained
Fracture
Conchoidal
Irregular
Porosity
Very Less Porous
Less Porous
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
Resistance
Heat Resistant, Impact Resistant
Heat Resistant, Impact Resistant
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
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
Obsidian vs Porphyry Characteristics
Though some rocks look identical, they have certain characteristics which distinguish them from others. Characteristics of rocks include texture, appearance, color, fracture, streak, hardness etc. Obsidian vs Porphyry characteristics assist us to distinguish and recognize rocks. Also you can check about Properties of Obsidian and Properties of Porphyry. Learn more about Obsidian vs Porphyry in the next section. The interior uses of Obsidian include Decorative aggregates and Interior decoration whereas the interior uses of Porphyry include Decorative aggregates and Interior decoration. Due to some exceptional properties of Obsidian and Porphyry, they have various applications in construction industry. The uses of Obsidian in construction industry include Arrowheads, Cutting tool, Knives, Scrapers, Spear points and that of Porphyry include Construction aggregate.
More about Obsidian and Porphyry
Here you can know more about Obsidian and Porphyry. The life cycle of a rock consists of formation of rock, composition of rock and transformation of rock. The composition of Obsidian and Porphyry consists of mineral content and compound content. The mineral content of Obsidian includes and mineral content of Porphyry includes Biotite, Chert, Feldspar, Garnet, Graphite, Quartz, Silica. You can also check out the list of all Igneous Rocks. When we have to compare Obsidian vs Porphyry, the texture, color and appearance plays an important role in determining the type of rock. Obsidian is available in black, blue, brown, green, orange, red, tan, yellow colors whereas, Porphyry is available in black, brown, green, grey, red, rust, white colors. Appearance of Obsidian is Shiny and that of Porphyry is Dull. Properties of rock is another aspect for Obsidian vs Porphyry. The hardness of Obsidian is 5-5.5 and that of Porphyry is 6-7. The types of Obsidian are Fireworks Obsidian, Mahogany, Sheen Obsidian, Snowflake obsidian and Velvet Peacock Obsidian whereas types of Porphyry are Rhomb Porphyry. Streak of rock is the color of powder produced when it is dragged across an unweathered surface. The streak of Obsidian and Porphyry is white. The specific heat capacity of Obsidian is 0.92 kJ/Kg K and that of Porphyry is 0.71 kJ/Kg K. Depending on the properties like hardness, toughness, specific heat capacity, porosity etc., rocks are resistant to heat, wear, impact, etc.Obsidian is heat resistant, impact resistant whereas Porphyry is heat resistant, impact resistant.