Definition
Dacite is a volcanic igneous rock which is rintermediate in composition between andesite 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
Origin
Romania and Moldova, Europe
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Discoverer
Unknown
Unknown
Etymology
From Dacia, a province of the Roman Empire which lay between the Danube River and Carpathian Mountains where the rock was first described
From the Middle High German verb gneist (to spark; so called because the rock glitters)
Class
Igneous Rocks
Metamorphic Rocks
Sub-Class
Durable Rock, Soft Rock
Durable Rock, Hard Rock
Other Categories
Fine Grained Rock, Medium Grained Rock, Opaque Rock
Coarse Grained Rock, Medium Grained Rock, Opaque Rock
Texture
Aphanitic to Porphyritic
Banded, Foliated, Platy
Color
Bluish - Grey, Brown, Grey, Light to Dark Grey
Black, Brown, Pink, Red, White
Durability
Durable
Durable
Appearance
Vesicular
Foliated
Interior Uses
Decorative Aggregates, Entryways, Interior Decoration
Countertops, Decorative Aggregates, Flooring, Interior Decoration
Exterior Uses
As Building Stone, Paving 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
Antiquity Uses
Artifacts
Artifacts
Commercial Uses
Commemorative Tablets, Creating Artwork
Cemetery Markers, Jewelry, Tombstones, Used in aquariums
Types
Footwall Dacite, Hanging wall Dacite, Tuff and Biotite Dacite
Augen Gneiss, Henderson Gneiss, Lewisian Gneiss, Archean and Proterozoic Gneiss.
Features
Host Rock for Lead, Is one of the oldest rock
Generally rough to touch, Is one of the oldest rock
Archaeological Significance
Famous Monuments
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Konark Sun Temple in India, Washington Monument, US
Formation
Dacitic magma is formed by the subduction of young oceanic crust under a thick felsic continental plate. Further, the Oceanic crust is hydrothermally altered as quartz and sodium are added.
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, Mg, 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
Impact Metamorphism
Types of Weathering
Biological Weathering, Chemical Weathering, Mechanical Weathering
Biological Weathering, Mechanical Weathering
Types of Erosion
Chemical Erosion
Chemical Erosion, Coastal Erosion, Sea Erosion
Grain Size
Medium to Fine Coarse Grained
Medium to Coarse Grained
Fracture
Conchoidal
Irregular
Porosity
Less Porous
Very Less Porous
Luster
Subvitreous to Dull
Dull
Specific Gravity
2.86-2.87
2.5-2.7
Transparency
Translucent
Translucent to Opaque
Density
2.77-2.771 g/cm3
2.6-2.9 g/cm3
Resistance
Heat Resistant, Impact Resistant, Pressure Resistant, Wear Resistant
Heat Resistant, Pressure Resistant, Scratch Resistant, Wear Resistant
Deposits in Eastern Continents
Asia
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China, India, Iran, Iraq, Kazakhstan, Kyrgyzstan, Mongolia, Russia
Africa
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Cameroon, Ethiopia, Ghana, Kenya, Madagascar, Morocco, Mozambique, Namibia, Nigeria, Tanzania, Togo
Europe
France, Greece, Romania, Scotland, Spain
Albania, Austria, Bosnia and Herzegovina, Finland, France, Georgia, Germany, Hungary, Italy, Kosovo, Monaco, Norway, Poland, Romania, Serbia, Slovakia, Slovenia, Switzerland, Ukraine, United Kingdom
Deposits in Western Continents
North America
USA
Canada, Costa Rica, Cuba, Mexico, Panama, USA
South America
Argentina, Bolivia, Chile, Colombia, Ecuador, Peru, Venezuela
Argentina, Bolivia, Brazil, Chile, Colombia, Ecuador, Peru, Venezuela
Deposits in Oceania Continent
Australia
New Zealand, South Australia, Western Australia
New South Wales, New Zealand, Queensland, Victoria