What minerals are in Komatiite?
Komatiite:
- An ultramafic, volcanic rock that is primarily composed of the minerals pyroxene and olivine.
- A very unusual and rare volcanic rock type that is not produced today.
- A rock type whose hotly– and wetly– debated origin sometimes galvanizes geologists to shouting matches, fist fights, and drinking contests.
Is Komatiite an igneous rock?
They are one variety of extrusive ultramafic igneous rock (although a komatiite in Canada has been interpreted to be an intrusive sill). Komatiite is an exceedingly rare type of lava. No volcano on Earth erupts this material today.
How is spinifex texture formed?
The distinctive spinifex texture is formed by skeletal, platy, or acicular crystals of olivine, orthopyroxene, or clinopyroxene, or their pseudomorphs in ultramafic and mafic lavas or silicate-rich furnace slag. The complex skeletal or platy crystals may show random orientation, or may display a preferred arrangement.
What are ultramafic rocks made of?
Ultramafic metamorphic rocks result from the metamorphism of mantle rocks and some oceanic crust and contain dominantly magnesium, silicon, and carbon dioxide, with smaller amounts of iron, calcium, and aluminum.
Are ultramafic rocks rare?
Ultramafic rocks are dominated by olivine or olivine and pyroxene. Such rocks are rare on the Earth’s surface, but they dominate the mantle.
What minerals does basalt contain?
Common minerals in basalt include olivine, pyroxene, and plagioclase. Basalt is erupted at temperatures between 1100 to 1250 ° C. Volcanic rock (or lava) that characteristically is dark in color (gray to black), contains 45 to 53 percent silica, and is rich in iron and magnesium.
What type of rock is Komatiite?
Komatiite, a magnesium-rich, high-temperature volcanic rock derived from very hot mantle (part of the Earth between the crust and the core), was extruded in abundance during the early Precambrian when the heat flow of the Earth was higher than it is today.
How can you tell an ultramafic rock?
Ultramafic rocks are usually defined by their modal mineralogy. They have a color index greater than 90, where the term “color index” refers to the percentage of mafic minerals such as olivine and pyroxene present in the rock.
Is basalt rock hard?
Basalt is a hard, black volcanic rock with less than about 52 weight percent silica (SiO2). Because of basalt’s low silica content, it has a low viscosity (resistance to flow). Common minerals in basalt include olivine, pyroxene, and plagioclase. Basalt is erupted at temperatures between 1100 to 1250 ° C.
What kind of rocks are the komatiites made of?
Komatiites are fascinating volcanic rocks. They are among the most ancient lavas of the Earth following the 3.8 Ga pillow basalts at Isua and they represent some of the oldest ultramafic magmatic rocks preserved in the Earth’s crust at 3.5 Ga.
What kind of texture does a komatiite lava have?
Komatiite lavas are famous for their unique olivine spinifex and cumulate crystal textures and internal textural zonation. In komatiitic basalts, such textures can also involve pyroxene. Zone A: characterized by spinifex-textured rock.
Where are komatiites found on the earth’s surface?
Lower temperature mantle melts such as basalt and picrite have essentially replaced komatiites as an eruptive lava on the Earth’s surface. Geographically, komatiites are predominantly restricted in distribution to the Archaean shield areas, and occur with other ultramafic and high-magnesian mafic volcanic rocks in Archaean greenstone belts.
What are the blades of a komatiite made of?
In the spinifex-textured komatiites, elongate and skeletal olivine (or pyroxene in komatiitic basalts) blades ranging in length from mm to tens of cm are set in a fine-grained matrix that originally contained a large proportion of volcanic glass ranging in composition from komatiite to komatiitic basalt. Origin of spinifex texture