Definition
Gneiss is a common and widely distributed type of rock formed by high-grade regional metamorphic processes from pre-existing formations that were originally either igneous or sedimentary rocks
  
Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption
  
History
  
  
Origin
Unknown
  
Italy
  
Discoverer
Unknown
  
Unknown
  
Etymology
From the Middle High German verb gneist (to spark; so called because the rock glitters)
  
From a Latin word tophous then in Italian tufo and finally tuff
  
Class
Metamorphic Rocks
  
Igneous Rocks
  
Sub-Class
Durable Rock, Hard Rock
  
Durable Rock, Medium Hardness Rock
  
Family
  
  
Group
Not Applicable
  
Volcanic
  
Other Categories
Coarse Grained Rock, Medium Grained Rock, Opaque Rock
  
Fine Grained Rock, Opaque Rock
  
Texture
Banded, Foliated, Platy
  
Clastic, Pyroclastic
  
Color
Black, Brown, Pink, Red, White
  
Brown, Grey, Yellow
  
Maintenance
More
  
More
  
Durability
Durable
  
Durable
  
Water Resistant
Yes
  
Yes
  
Scratch Resistant
Yes
  
Yes
  
Stain Resistant
Yes
  
No
  
Wind Resistant
Yes
  
No
  
Acid Resistant
No
  
No
  
Appearance
Foliated
  
Dull, Vesicular and Foilated
  
Architecture
  
  
Interior Uses
Countertops, Decorative Aggregates, Flooring, Interior Decoration
  
Decorative Aggregates, Entryways, Flooring, Homes, Interior Decoration
  
Exterior Uses
As Building Stone, As Facing Stone, Garden Decoration, Paving Stone
  
As Building Stone, As Facing Stone, Garden Decoration, Office Buildings, Paving Stone
  
Other Architectural Uses
Curbing
  
Curbing
  
Industry
  
  
Construction Industry
As Dimension Stone
  
Building houses or walls, Construction Aggregate
  
Medical Industry
Not Yet Used
  
Not Yet Used
  
Antiquity Uses
Artifacts
  
Artifacts, Monuments, Sculpture, Small Figurines
  
Other Uses
  
  
Commercial Uses
Cemetery Markers, Jewelry, Tombstones, Used in aquariums
  
Creating Artwork
  
Types
Augen Gneiss, Henderson Gneiss, Lewisian Gneiss, Archean and Proterozoic Gneiss.
  
Welded tuff, Rhyolitic tuff, Basaltic tuff, Trachyte tuff, Andesitic tuff and Ignimbrite.
  
Features
Generally rough to touch, Is one of the oldest rock
  
Always found as volcanic pipes over deep continental crust
  
Archaeological Significance
  
  
Monuments
Used
  
Used
  
Famous Monuments
Konark Sun Temple in India, Washington Monument, US
  
Easter Island in the Polynesian Triangle, Pacific Ocean
  
Sculpture
Not Yet Used
  
Used
  
Famous Sculptures
Not Applicable
  
Data Not Available
  
Pictographs
Not Used
  
Used
  
Petroglyphs
Not Used
  
Used
  
Figurines
Not Yet Used
  
Used
  
Fossils
Absent
  
Absent
  
Formation
Gneiss is a high grade metamorphic rock i.e. it has been subjected to higher temperatures and pressures than schist. It is formed by the metamorphosis of Gneiss forms from volcanic rock, shale or granitie.
  
Tuff is formed when large masses of ash and sand which are mixed with hot gases are ejected by a volcano and avalanche rapidly down its slopes.
  
Composition
  
  
Mineral Content
Biotite, Chlorite, Feldspar, Garnet, Graphite, Hornblade, Micas, Muscovite or Illite, Quartz, Quartzite, Silica, Zircon
  
Calcite, Chlorite
  
Compound Content
Aluminium Oxide, NaCl, CaO, Iron(III) Oxide, FeO, Potassium Oxide, Magnesium Carbonate, MgO, MnO, Phosphorus Pentoxide, Silicon Dioxide, Titanium Dioxide
  
Hydrogen Sulfide, Sulfur Dioxide
  
Transformation
  
  
Metamorphism
Yes
  
Yes
  
Types of Metamorphism
Impact Metamorphism
  
Burial Metamorphism, Cataclastic Metamorphism, Contact Metamorphism, Hydrothermal Metamorphism, Impact Metamorphism, Regional Metamorphism
  
Weathering
Yes
  
Yes
  
Types of Weathering
Biological Weathering, Mechanical Weathering
  
Biological Weathering, Chemical Weathering, Mechanical Weathering
  
Erosion
Yes
  
Yes
  
Types of Erosion
Chemical Erosion, Coastal Erosion, Sea Erosion
  
Chemical Erosion, Coastal Erosion, Glacier Erosion, Sea Erosion, Water Erosion, Wind Erosion
  
Physical Properties
  
  
Hardness
7
  
4-6
  
Grain Size
Medium to Coarse Grained
  
Fine Grained
  
Fracture
Irregular
  
Uneven
  
Streak
White
  
White
  
Porosity
Very Less Porous
  
Highly Porous
  
Luster
Dull
  
Vitreous to Dull
  
Compressive Strength
125.00 N/mm2
  
17
243.80 N/mm2
  
5
Cleavage
Poor
  
Not Available
  
Toughness
1.2
  
Not Available
  
Specific Gravity
2.5-2.7
  
2.73
  
Transparency
Translucent to Opaque
  
Opaque
  
Density
2.6-2.9 g/cm3
  
1-1.8 g/cm3
  
Thermal Properties
  
  
Specific Heat Capacity
Not Available
  
0.20 kJ/Kg K
  
25
Resistance
Heat Resistant, Pressure Resistant, Scratch Resistant, Wear Resistant
  
Heat Resistant, Impact Resistant, Pressure Resistant, Wear Resistant
  
Deposits in Eastern Continents
  
  
Asia
China, India, Iran, Iraq, Kazakhstan, Kyrgyzstan, Mongolia, Russia
  
Afghanistan, Armenia, Azerbaijan, Burma, Cambodia, China, India, Indonesia, Iran, Japan, Malaysia, Mongolia, Nepal, North Korea, Pakistan, Saudi Arabia, Syria, Taiwan, Thailand, Turkey, Vietnam, Yemen
  
Africa
Cameroon, Ethiopia, Ghana, Kenya, Madagascar, Morocco, Mozambique, Namibia, Nigeria, Tanzania, Togo
  
Cameroon, Cape Verde, Eritrea, Ethiopia, Kenya, Libya, Madagascar, Nigeria, Rwanda, South Africa, Sudan, Uganda
  
Europe
Albania, Austria, Bosnia and Herzegovina, Finland, France, Georgia, Germany, Hungary, Italy, Kosovo, Monaco, Norway, Poland, Romania, Serbia, Slovakia, Slovenia, Switzerland, Ukraine, United Kingdom
  
France, Georgia, Germany, Greece, Iceland, Italy, Netherlands, Poland, Portugal, Spain, United Kingdom
  
Others
Not Yet Found
  
Antarctica, Hawaii Islands
  
Deposits in Western Continents
  
  
North America
Canada, Costa Rica, Cuba, Mexico, Panama, USA
  
Canada, Costa Rica, Panama, USA
  
South America
Argentina, Bolivia, Brazil, Chile, Colombia, Ecuador, Peru, Venezuela
  
Argentina, Bolivia, Brazil, Chile, Ecuador, Paraguay
  
Deposits in Oceania Continent
  
  
Australia
New South Wales, New Zealand, Queensland, Victoria
  
Central Australia, Western Australia