Definition
Rhyodacite is an extrusive volcanic rock intermediate in composition between dacite and rhyolite
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
Discoverer
Unknown
Unknown
Etymology
Rhyo lite + dacite : a rock intermediate between rhyolite and dacite that is the extrusive equivalent of granodiorite
From the Middle High German verb gneist (to spark; so called because the rock glitters)
Class
Igneous Rocks
Metamorphic Rocks
Sub-Class
Durable Rock, Medium Hardness Rock
Durable Rock, Hard Rock
Group
Volcanic
Not Applicable
Other Categories
Fine Grained Rock, Opaque Rock
Coarse Grained Rock, Medium Grained Rock, Opaque Rock
Texture
Earthy
Banded, Foliated, Platy
Color
Black to Grey, Dark Greenish - Grey
Black, Brown, Pink, Red, White
Durability
Durable
Durable
Scratch Resistant
Yes
Yes
Appearance
Skeletal
Foliated
Interior Uses
Decorative Aggregates, Interior Decoration
Countertops, Decorative Aggregates, Flooring, Interior Decoration
Exterior Uses
As Building Stone, Garden Decoration
As Building Stone, As Facing Stone, Garden Decoration, Paving Stone
Other Architectural Uses
Curbing
Curbing
Construction Industry
As Dimension Stone, Construction Aggregate, for Road Aggregate, Landscaping
As Dimension Stone
Medical Industry
Not Yet Used
Not Yet Used
Antiquity Uses
Artifacts
Artifacts
Commercial Uses
Cemetery Markers, Creating Artwork
Cemetery Markers, Jewelry, Tombstones, Used in aquariums
Types
Not Available
Augen Gneiss, Henderson Gneiss, Lewisian Gneiss, Archean and Proterozoic Gneiss.
Features
Available in Lots of Colors and Patterns
Generally rough to touch, Is one of the oldest rock
Archaeological Significance
Monuments
Not Yet Used
Used
Famous Monuments
Not Applicable
Konark Sun Temple in India, Washington Monument, US
Sculpture
Not Yet Used
Not Yet Used
Famous Sculptures
Not Applicable
Not Applicable
Pictographs
Used
Not Used
Petroglyphs
Used
Not Used
Figurines
Not Yet Used
Not Yet Used
Formation
Rhyodacite is a fine-grained, hard rock which is a type of metasomatite, essentially altered basalt. It forms with or without crystallization, either below the surface as intrusive rocks or on the surface as extrusive rocks.
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.
Mineral Content
Amphibole, Apatite, Biotite, Feldspar, Garnet, Hornblade, Magnetite, Plagioclase, Pyroxene, Quartz, Zircon
Biotite, Chlorite, Feldspar, Garnet, Graphite, Hornblade, Micas, Muscovite or Illite, Quartz, Quartzite, Silica, Zircon
Compound Content
Ca, Fe, Potassium Oxide, NA, Potassium, Silicon Dioxide
Aluminium Oxide, NaCl, CaO, Iron(III) Oxide, FeO, Potassium Oxide, Magnesium Carbonate, MgO, MnO, Phosphorus Pentoxide, Silicon Dioxide, Titanium Dioxide
Types of Metamorphism
Burial Metamorphism, Cataclastic Metamorphism, Contact Metamorphism, Hydrothermal Metamorphism, Impact Metamorphism, Regional Metamorphism
Impact Metamorphism
Types of Weathering
Biological Weathering, Chemical Weathering, Mechanical Weathering
Biological Weathering, Mechanical Weathering
Types of Erosion
Chemical Erosion, Coastal Erosion, Glacier Erosion
Chemical Erosion, Coastal Erosion, Sea Erosion
Grain Size
Fine Grained
Medium to Coarse Grained
Fracture
Conchoidal
Irregular
Porosity
Less Porous
Very Less Porous
Luster
Greasy to Dull
Dull
Cleavage
Not Available
Poor
Specific Gravity
2.34-2.40
2.5-2.7
Transparency
Opaque
Translucent to Opaque
Density
Not Available
2.6-2.9 g/cm3
Specific Heat Capacity
Not Available
Resistance
Heat Resistant
Heat Resistant, Pressure Resistant, Scratch Resistant, Wear Resistant
Deposits in Eastern Continents
Asia
China, India, Iran, Saudi Arabia, Sri Lanka, Taiwan, Thailand, Turkey, Vietnam
China, India, Iran, Iraq, Kazakhstan, Kyrgyzstan, Mongolia, Russia
Africa
Angola, Egypt, Madagascar, Namibia, Nigeria, South Africa
Cameroon, Ethiopia, Ghana, Kenya, Madagascar, Morocco, Mozambique, Namibia, Nigeria, Tanzania, Togo
Europe
Austria, Belgium, Finland, France, Germany, Italy, Norway, Sardinia, Spain, Switzerland
Albania, Austria, Bosnia and Herzegovina, Finland, France, Georgia, Germany, Hungary, Italy, Kosovo, Monaco, Norway, Poland, Romania, Serbia, Slovakia, Slovenia, Switzerland, Ukraine, United Kingdom
Others
Not Yet Found
Not Yet Found
Deposits in Western Continents
North America
Canada, USA
Canada, Costa Rica, Cuba, Mexico, Panama, USA
South America
Not Yet Found
Argentina, Bolivia, Brazil, Chile, Colombia, Ecuador, Peru, Venezuela
Deposits in Oceania Continent
Australia
Not Yet Found
New South Wales, New Zealand, Queensland, Victoria