How old are komatiites?
–2.5 billion years ago
Komatiites are rare rocks; almost all komatiites were formed during the Archaean Eon (4.0–2.5 billion years ago), with few younger (Proterozoic or Phanerozoic) examples known. This restriction in age is thought to be due to cooling of the mantle, which may have been 100–250 °C (212–482 °F) hotter during the Archaean.
Why do komatiites not form anymore?
The interior of the Earth might not be hot enough to produce many (if any) komatiites, and definitely not at the rate it was back when the Earth was only 1 or 2 billion years old.
Who discovered komatiite?
Komatiites were first identified by Richard and Morris Viljoen in 1969, in the Archean greenstone belt in the Barberton Mountain land of South Africa as a distinctive and “new” class of magnesium-rich (20-30 wt % MgO) volcanic rocks.
What color is komatiite?
This should discriminate some picrites without the corresponding texture to be classified as komatiites. Colour Black, grey, locally grey-green. Structure Pillow-like, porphyric, spinifex. Texture Porphyric – spinifex.
Why are greenstone belts green?
The name comes from the green hue imparted by the colour of the metamorphic minerals within the mafic rocks: the typical green minerals are chlorite, actinolite, and other green amphiboles. Greenstone belts also often contain ore deposits of gold, silver, copper, zinc and lead.
Why is erebor green?
This is because the temperatures and pressures needed to produce greenschist from underwater lava flow deposits makes the rock easily penetrable by gold-rich fluid. This makes Erebor a beautiful, green, gold-rich environment.
What is tuff rock?
Tuff is volcaniclastic rock composed of solid volcanic ash that may contain particles of volcanic glass (vitro-clasts), small fragments of crystals formed in lava (crystal clasts) and/or fragments of volcanic rock and lava (lithoclasts).
What is the mineral content of diorite?
Diorite
| Type | Igneous Rock |
|---|---|
| Color | Approximately half dark, half white minerals |
| Mineral Composition | Sodium – Calcium Plagioclase, Quartz, Hornblende, Biotite |
| Miscellaneous | Salt and Pepper Appearance |
| Tectonic Environment | Convergent Boundary – Intruded into batholiths above Island Arc-type Subduction Zone |
What is the cooling rate of komatiite?
Donaldson (1982) estimated that cooling rates in the A3 layer of a typical 5–10 m thick komatiite flow were <1 C/h. In contrast, to reproduce the dendritic mor- phology of platy spinifex olivine crystals in normal dynamic cooling laboratory experiments requires cooling rates >50 C/h (Donaldson, 1982).
What is the texture of komatiite?
Komatiites and variolitic basalts are widespread in Archean volcanic sequences. Spinifex is a spectacular bladed olivine or pyroxene texture that characterizes komatiite, a rock almost exclusively restricted to the Archean; varioles are cm-scale leucocratic globular structures abundant in many Archean basalts.
How do you identify pyroxenite?
There are three type of pyroxenite rock that areclinopyroxenites, orthopyroxenites, and the websterites.
- Color: Light green, dark green, or black.
- Protolith or Parent Rock:
- Hardness: 5 to 7.
- Grain size: Coarse-grained texture.
- Group: Ultramafic igneous rock.
What is the parent rock of greenstone?
Greenstone
| Type | Metamorphic Rock |
|---|---|
| Metamorphic Type | Regional |
| Metamorphic Grade | Low Grade (Low P – Low T) |
| Parent Rock | Basalt; Mafic igneous rocks |
| Metamorphic Environment | Low grade regional metamorphism along a convergent plate boundary |
Is gold found in greenstone?
Greenstone belts are zones of parallel rocks that include these meta-basalt rocks and a variety of associated formations. These four greenstones are from gold deposits located all around the world, and show how common this type of deposit is.
Who rules the Lonely Mountain after Thorin dies?
After the death of Thorin in the Battle of Five Armies, Dain becomes King under the Mountain. He redeems the Arkenstone from Bard with a fourteenth of the treasure, which is used to re-establish Dale. Over the next three years, Bard rebuilds the city of Dale and becomes its ruler. The city begins to prosper again.
What is tuff made from?
What is the chemical composition of tuff?
The yellow tuff, considered to be the weathering product of the black tuff, contains only 4% volcanic glass and 21% primary minerals, 8% Fe-rich minerals, 51% amorphous material identified as halloysite-like allophane, 15% halloysite, and 5% hydroxyapatite.