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
  
Hornfels is a metamorphic rock formed by the contact between mudstone or other clay rich rock, and a hot igneous body, and represents a heat altered equivalent of the original rock
  
History
  
  
Origin
Ethiopia
  
New Zealand
  
Discoverer
Obsius
  
Unknown
  
Etymology
From Latin obsidianus, misprint of Obsianus (lapis) (stone) of Obsius
  
From German which means hornstone
  
Class
Igneous Rocks
  
Metamorphic Rocks
  
Sub-Class
Durable Rock, Medium Hardness Rock
  
Durable Rock, Soft Rock
  
Family
  
  
Group
Volcanic
  
Not Applicable
  
Other Categories
Opaque Rock
  
Fine Grained Rock, Opaque Rock
  
Texture
Glassy
  
Granular, Platy
  
Color
Black, Blue, Brown, Green, Orange, Red, Tan, Yellow
  
Brown, Dark Greenish - Grey, Green, Reddish Brown
  
Maintenance
Less
  
Less
  
Durability
Durable
  
Durable
  
Water Resistant
Yes
  
Yes
  
Scratch Resistant
Yes
  
No
  
Stain Resistant
No
  
No
  
Wind Resistant
No
  
No
  
Acid Resistant
No
  
No
  
Appearance
Shiny
  
Dull
  
Architecture
  
  
Interior Uses
Decorative Aggregates, Interior Decoration
  
Decorative Aggregates, Flooring, Homes, Interior Decoration
  
Exterior Uses
Garden Decoration
  
As Building Stone, As Facing Stone, Garden Decoration, Office Buildings, Paving Stone
  
Other Architectural Uses
Not Yet Used
  
Curbing
  
Industry
  
  
Construction Industry
Arrowheads, Cutting Tool, Knives, Scrapers, Spear Points
  
for Road Aggregate, Roadstone
  
Medical Industry
Surgery
  
Not Yet Used
  
Antiquity Uses
Artifacts, Jewellery
  
Artifacts, Monuments
  
Other Uses
  
  
Commercial Uses
Creating Artwork, Mirror, Used in aquariums
  
Cemetery Markers, Commemorative Tablets, Creating Artwork
  
Types
Fireworks Obsidian, Mahogany, Sheen Obsidian, Snowflake obsidian and Velvet Peacock Obsidian
  
Biotite hornfels
  
Features
Blocks negativity, Helps to protect against depression
  
Smooth to touch
  
Archaeological Significance
  
  
Monuments
Not Yet Used
  
Used
  
Famous Monuments
Not Applicable
  
Data Not Available
  
Sculpture
Not Yet Used
  
Not Yet Used
  
Famous Sculptures
Not Applicable
  
Not Applicable
  
Pictographs
Used
  
Used
  
Petroglyphs
Used
  
Used
  
Figurines
Not Yet Used
  
Not Yet Used
  
Fossils
Absent
  
Absent
  
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.
  
Due to change in environmental conditions, rocks are heated and pressurized deep inside the Earth's surface. Hornfels is formed from the extreme heat caused by magma or by the intense collisions and friction of tectonic plates.
  
Composition
  
  
Mineral Content
Not Available
  
Andalusite
  
Compound Content
Aluminium Oxide, CaO, Iron(III) Oxide, FeO, Potassium Oxide, MgO, MnO, Sodium Oxide, Phosphorus Pentoxide, Silicon Dioxide, Titanium Dioxide
  
Fe, Mg
  
Transformation
  
  
Metamorphism
Yes
  
No
  
Types of Metamorphism
Burial Metamorphism, Cataclastic Metamorphism, Contact Metamorphism
  
Not Applicable
  
Weathering
Yes
  
Yes
  
Types of Weathering
Biological Weathering, Chemical Weathering, Mechanical Weathering
  
Biological Weathering
  
Erosion
Yes
  
Yes
  
Types of Erosion
Chemical Erosion, Coastal Erosion, Glacier Erosion
  
Chemical Erosion, Glacier Erosion, Sea Erosion, Water Erosion, Wind Erosion
  
Physical Properties
  
  
Hardness
5-5.5
  
2-3
  
Grain Size
Not Applicable
  
Fine Grained
  
Fracture
Conchoidal
  
Conchoidal
  
Streak
White
  
Unknown
  
Porosity
Very Less Porous
  
Highly Porous
  
Luster
Vitreous
  
Shiny
  
Cleavage
Non-Existent
  
Perfect
  
Toughness
Not Available
  
Not Yet Found
  
Specific Gravity
2.6-2.7
  
3.4-3.9
  
Transparency
Translucent
  
Opaque
  
Density
2.6 g/cm3
  
0.25-0.30 g/cm3
  
Thermal Properties
  
  
Specific Heat Capacity
0.92 kJ/Kg K
  
10
0.84 kJ/Kg K
  
15
Resistance
Heat Resistant, Impact Resistant
  
Heat Resistant, Impact Resistant, Pressure Resistant
  
Deposits in Eastern Continents
  
  
Asia
Afghanistan, Indonesia, Japan, Russia
  
Bangladesh, Bhutan, China, India, North Korea, Qatar, Russia, Saudi Arabia, South Korea, Thailand
  
Africa
Kenya
  
Cameroon, East Africa, Tanzania, Western Africa
  
Europe
Greece, Hungary, Iceland, Italy, Turkey
  
United Kingdom
  
Others
Not Yet Found
  
Not Yet Found
  
Deposits in Western Continents
  
  
North America
Canada, Mexico, USA
  
Canada, USA
  
South America
Argentina, Chile, Ecuador, Peru
  
Bolivia, Brazil, Colombia, Ecuador
  
Deposits in Oceania Continent
  
  
Australia
New Zealand
  
New South Wales, New Zealand, Queensland, Western Australia