Post by 1dave on Oct 1, 2022 18:44:52 GMT -5
Magma elements change over time. They begin heavy in Mantle elements and slowly mutate into crust elements.
en.wikipedia.org/wiki/Komatiite
Komatiites have a distinctive texture known as spinifex texture. It consists of long acicular phenocrysts of olivine or pyroxene which give the rock a bladed appearance especially on a weathered surface. Spinifex texture is the result of rapid crystallization of highly magnesian liquid.
Basalt is extremely fluid and cover large areas. Wet areas will fill the basalt with smooth domed gas bubbles that solidify and later fill with other minerals to become geodes.
Andesite is less fluid, more large crystals form, giving gas bubbles a rugged exterior to geodes that form in it.
Rhyolite tends to build domes instead of flowing. The high silica content can build spheroids and lithophasae (rock bubbles) known as thundereggs.
A closer look at how the element makeup changes over time.
The oxygen content remains almost constant. The amount of silica steadily rises. The amount of magnesium drops rapidly, iron drops slowly, while the other minerals slowly rise.
Other ways of looking at the whole process.
en.wikipedia.org/wiki/Komatiite
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.[4][5] The early Earth had much higher heat production, due to the residual heat from planetary accretion, as well as the greater abundance of radioactive isotopes, particularly shorter lived ones like uranium 235 which produce more decay heat. Lower temperature mantle melts such as basalt and picrite have essentially replaced komatiites as an eruptive lava on the Earth's surface.
Komatiites have a distinctive texture known as spinifex texture. It consists of long acicular phenocrysts of olivine or pyroxene which give the rock a bladed appearance especially on a weathered surface. Spinifex texture is the result of rapid crystallization of highly magnesian liquid.
Basalt is extremely fluid and cover large areas. Wet areas will fill the basalt with smooth domed gas bubbles that solidify and later fill with other minerals to become geodes.
Andesite is less fluid, more large crystals form, giving gas bubbles a rugged exterior to geodes that form in it.
Rhyolite tends to build domes instead of flowing. The high silica content can build spheroids and lithophasae (rock bubbles) known as thundereggs.
A closer look at how the element makeup changes over time.
The oxygen content remains almost constant. The amount of silica steadily rises. The amount of magnesium drops rapidly, iron drops slowly, while the other minerals slowly rise.
Other ways of looking at the whole process.
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