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
Banded iron formation are distinctive units of sedimentary rock that are almost always of Precambrian age
History
Origin
Ethiopia
Western Australia, Minnesota
Discoverer
Obsius
Johann Gottlob Lehmann
Etymology
From Latin obsidianus, misprint of Obsianus (lapis) (stone) of Obsius
From its formation process
Class
Igneous Rocks
Sedimentary Rocks
Sub-Class
Durable Rock, Medium Hardness Rock
Durable Rock, Medium Hardness Rock
Family
Group
Volcanic
-
Other Categories
Opaque Rock
Coarse Grained Rock, Opaque Rock
Texture
Glassy
Banded, Trellis
Color
Black, Blue, Brown, Green, Orange, Red, Tan, Yellow
Red, Reddish Brown
Maintenance
Less
Less
Durability
Durable
Durable
Water Resistant
✔
✘
✔
✘
Scratch Resistant
✔
✘
✔
✘
Stain Resistant
✔
✘
✔
✘
Wind Resistant
✔
✘
✔
✘
Acid Resistant
✔
✘
✔
✘
Appearance
Shiny
Layered, Banded, Veined and Shiny
Architecture
Interior Uses
Decorative Aggregates, Interior Decoration
Decorative Aggregates, Homes
Exterior Uses
Garden Decoration
Paving Stone, Office Buildings
Other Architectural Uses
-
Curbing, Whetstones
Industry
Construction Industry
Arrowheads, Cutting Tool, Knives, Scrapers, Spear Points
As Dimension Stone, Used for flooring, stair treads, borders and window sills.
Medical Industry
Surgery
-
Antiquity Uses
Artifacts, Jewellery
Artifacts
Other Uses
Commercial Uses
Creating Artwork, Mirror, Used in aquariums
As a touchstone, Cemetery Markers, Creating Artwork
Types
Fireworks Obsidian, Mahogany, Sheen Obsidian, Snowflake obsidian and Velvet Peacock Obsidian
Algoma-type , Lake Superior-type, Superior-type and Taconite
Features
Blocks negativity, Helps to protect against depression
Is one of the oldest rock
Archaeological Significance
Monuments
-
-
Famous Monuments
-
-
Sculpture
-
-
Famous Sculptures
-
-
Pictographs
-
-
Petroglyphs
-
-
Figurines
-
-
Fossils
Absent
Present
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.
The banded iron layers are formed in sea water when oxygen is released by photosynthetic cyano-bacteria. The oxygen then combines with dissolved iron in ocean to form insoluble iron oxides, which precipitated out, forming a thin layer of banded iron formation on ocean floor.
Composition
Mineral Content
-
Hematite, Magnetite, Quartz
Compound Content
Aluminium Oxide, CaO, Iron(III) Oxide, FeO, Potassium Oxide, MgO, MnO, Sodium Oxide, Phosphorus Pentoxide, Silicon Dioxide, Titanium Dioxide
Fe, Iron(III) Oxide, Silicon Dioxide
Transformation
Metamorphism
✔
✘
✔
✘
Types of Metamorphism
Burial Metamorphism, Cataclastic Metamorphism, Contact Metamorphism
-
Weathering
✔
✘
✔
✘
Types of Weathering
Biological Weathering, Chemical Weathering, Mechanical Weathering
Chemical Weathering
Erosion
✔
✘
✔
✘
Types of Erosion
Chemical Erosion, Coastal Erosion, Glacier Erosion
Coastal Erosion, Wind Erosion
Physical Properties
Hardness
5-5.55.5-6
1
7
👆🏻
Grain Size
-
Large and Coarse Grained
Fracture
Conchoidal
Uneven, Splintery or Conchoidal
Streak
White
White
Porosity
Very Less Porous
Highly Porous
Luster
Vitreous
Earthy
Compressive Strength
0.15 N/mm2220.00 N/mm2
0.15
450
👆🏻
Cleavage
-
-
Toughness
-
1.5
Specific Gravity
2.6-2.75.0-5.3
0
8.4
👆🏻
Transparency
Translucent
Translucent to Opaque
Density
2.6 g/cm3-9999 g/cm3
0
1400
👆🏻
Thermal Properties
Specific Heat Capacity
0.92 kJ/Kg K3.20 kJ/Kg K
0.14
3.2
👆🏻
Resistance
Heat Resistant, Impact Resistant
Heat Resistant, Impact Resistant, Pressure Resistant, Wear Resistant
Deposits in Eastern Continents
Asia
Afghanistan, Indonesia, Japan, Russia
China, India, Iran, Iraq, Oman, Russia, Saudi Arabia, Taiwan, Thailand, Vietnam
Africa
Kenya
Kenya, Morocco, South Africa, Tanzania
Europe
Greece, Hungary, Iceland, Italy, Turkey
Austria, France, Greece, Italy, Malta, Poland, Portugal, Serbia, Spain, Sweden, United Kingdom
Others
-
Greenland, Mid-Atlantic Ridge
Deposits in Western Continents
North America
Canada, Mexico, USA
Canada, Mexico, USA
South America
Argentina, Chile, Ecuador, Peru
Bolivia, Brazil
Deposits in Oceania Continent
Australia
New Zealand
New South Wales, Queensland, South Australia, Western Australia