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
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
-
New Zealand
Discoverer
Unknown
Unknown
Etymology
From the Middle High German verb gneist (to spark; so called because the rock glitters)
From German which means hornstone
Class
Metamorphic Rocks
Metamorphic Rocks
Sub-Class
Durable Rock, Hard Rock
Durable Rock, Soft Rock
Family
Group
-
-
Other Categories
Coarse Grained Rock, Medium Grained Rock, Opaque Rock
Fine Grained Rock, Opaque Rock
Texture
Banded, Foliated, Platy
Granular, Platy
Color
Black, Brown, Pink, Red, White
Brown, Dark Greenish - Grey, Green, Reddish Brown
Maintenance
More
Less
Durability
Durable
Durable
Water Resistant
✔
✘
✔
✘
Scratch Resistant
✔
✘
✔
✘
Stain Resistant
✔
✘
✔
✘
Wind Resistant
✔
✘
✔
✘
Acid Resistant
✔
✘
✔
✘
Appearance
Foliated
Dull
Architecture
Interior Uses
Countertops, Decorative Aggregates, Flooring, Interior Decoration
Decorative Aggregates, 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
for Road Aggregate, Roadstone
Medical Industry
-
-
Antiquity Uses
Artifacts
Artifacts, Monuments
Other Uses
Commercial Uses
Cemetery Markers, Jewelry, Tombstones, Used in aquariums
Cemetery Markers, Commemorative Tablets, Creating Artwork
Types
Augen Gneiss, Henderson Gneiss, Lewisian Gneiss, Archean and Proterozoic Gneiss.
Biotite hornfels
Features
Generally rough to touch, Is one of the oldest rock
Smooth to touch
Archaeological Significance
Monuments
-
-
Famous Monuments
Konark Sun Temple in India, Washington Monument, US
-
Sculpture
-
-
Famous Sculptures
-
-
Pictographs
-
-
Petroglyphs
-
-
Figurines
-
-
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.
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
Biotite, Chlorite, Feldspar, Garnet, Graphite, Hornblade, Micas, Muscovite or Illite, Quartz, Quartzite, Silica, Zircon
Andalusite
Compound Content
Aluminium Oxide, NaCl, CaO, Iron(III) Oxide, FeO, Potassium Oxide, Magnesium Carbonate, MgO, MnO, Phosphorus Pentoxide, Silicon Dioxide, Titanium Dioxide
Fe, Mg
Transformation
Metamorphism
✔
✘
✔
✘
Types of Metamorphism
Impact Metamorphism
-
Weathering
✔
✘
✔
✘
Types of Weathering
Biological Weathering, Mechanical Weathering
Biological Weathering
Erosion
✔
✘
✔
✘
Types of Erosion
Chemical Erosion, Coastal Erosion, Sea Erosion
Chemical Erosion, Glacier Erosion, Sea Erosion, Water Erosion, Wind Erosion
Physical Properties
Hardness
72-3
1
7
👆🏻
Grain Size
Medium to Coarse Grained
Fine Grained
Fracture
Irregular
Conchoidal
Streak
White
-
Porosity
Very Less Porous
Highly Porous
Luster
Dull
Shiny
Compressive Strength
125.00 N/mm25.80 N/mm2
0.15
450
👆🏻
Cleavage
-
Perfect
Toughness
1.2
-
Specific Gravity
2.5-2.73.4-3.9
0
8.4
👆🏻
Transparency
Translucent to Opaque
Opaque
Density
2.6-2.9 g/cm30.25-0.30 g/cm3
0
1400
👆🏻
Thermal Properties
Specific Heat Capacity
0.70 kJ/Kg K0.84 kJ/Kg K
0.14
3.2
👆🏻
Resistance
Heat Resistant, Pressure Resistant, Scratch Resistant, Wear Resistant
Heat Resistant, Impact Resistant, Pressure Resistant
Deposits in Eastern Continents
Asia
China, India, Iran, Iraq, Kazakhstan, Kyrgyzstan, Mongolia, Russia
Bangladesh, Bhutan, China, India, North Korea, Qatar, Russia, Saudi Arabia, South Korea, Thailand
Africa
Cameroon, Ethiopia, Ghana, Kenya, Madagascar, Morocco, Mozambique, Namibia, Nigeria, Tanzania, Togo
Cameroon, East Africa, Tanzania, Western Africa
Europe
Albania, Austria, Bosnia and Herzegovina, Finland, France, Georgia, Germany, Hungary, Italy, Kosovo, Monaco, Norway, Poland, Romania, Serbia, Slovakia, Slovenia, Switzerland, Ukraine, United Kingdom
United Kingdom
Others
-
-
Deposits in Western Continents
North America
Canada, Costa Rica, Cuba, Mexico, Panama, USA
Canada, USA
South America
Argentina, Bolivia, Brazil, Chile, Colombia, Ecuador, Peru, Venezuela
Bolivia, Brazil, Colombia, Ecuador
Deposits in Oceania Continent
Australia
New South Wales, New Zealand, Queensland, Victoria
New South Wales, New Zealand, Queensland, Western Australia