How spinifex texture form?
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.
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.
What type of rock is Komatiites?
ultramafic volcanic rocks
Komatiites are ultramafic volcanic rocks. An ultramafic rock is a rock that has very low silicon (SiO2), sodium (NaO), and potassium (K2O) and very high and iron (FeO) and magnesium (MgO) content, generally greater than 18 weight percent MgO*.
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.
Is komatiite intrusive or extrusive?
extrusive ultramafic igneous rock
Komatiites are very rare igneous rocks. They are one variety of extrusive ultramafic igneous rock (although a komatiite in Canada has been interpreted to be an intrusive sill). They are named after the Komati River in South Africa, the type locality. Komatiite is an exceedingly rare type of lava.
Is blue obsidian real?
Natural obsidian NEVER occurs in the colors transparent blue, red or yellow. These artificial products exist solely due to the inventiveness of humans and have nothing to do with obsidian !
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).
Is komatiite an igneous?
Komatiites are very rare igneous rocks. They are one variety of extrusive ultramafic igneous rock (although a komatiite in Canada has been interpreted to be an intrusive sill). They are named after the Komati River in South Africa, the type locality. Komatiite is an exceedingly rare type of lava.
Is red obsidian real?
Black is the most common color of obsidian. However, it can also be brown, tan, or green. Rarely, obsidian can be blue, red, orange, or yellow.
What is spinifex komatiite?
In their model, spinifex forms during the crystallization of hydrous, intrusive komatiite. Field studies by Dann (2000, 2001) have shown, however, that these komatiites, like those in most other areas, erupted as lava flows. Further comments on the wet komatiite hypothesis have been given by Arndt et al. (1998) and Arndt (2003).
What are the different types of komatiite flows?
Spinifex-textured komatiite flows are generally subdivided into three major units, as illustrated in Fig. 1. A thin (1–10 cm) olivine porphyritic upper chilled margin (A 1) is underlain by a ∼5–50 cm thick A 2 layer that consists of fine, skeletal and dendritic, randomly oriented olivine crystals embedded in a glassy matrix.
What are the habits of olivine crystals in komatiite?
Olivine in komatiite flows displays a wide variety of habits, from equant solid polyhedral crystals in the chilled margins and cumulate zones, to fine, randomly oriented skeletal grains in the uppermost part of the spinifex zone, and to large, complex dendritic crystals deeper in the flow ( Fig. 1 ).
What is an example of spinifex?
Spinifex is one of the most spectacular magmatic textures. The most striking examples comprise large olivine plates that form parts of giant, decimeter-sized dendritic crystals that are oriented perpendicular to the roof of the komatiitic unit ( Fig. 1 ).