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Magma rapidly cooled to below its normal crystallization temperature becomes a supercooled liquid, and, with further rapid cooling, this becomes an amorphous solid. The change from supercooled liquid to glass occurs at a temperature called the glass transition temperature, which depends on both cooling rate and the amount of water dissolved in ...
[4] [5] Such conventions include a constant cooling rate (20 kelvins per minute (36 °F/min)) [2] and a viscosity threshold of 10 12 Pa·s, among others. Upon cooling or heating through this glass-transition range, the material also exhibits a smooth step in the thermal-expansion coefficient and in the specific heat , with the location of these ...
Porphyritic texture develops when the larger crystals, called phenocrysts, grow to considerable size before the main mass of the magma crystallizes as finer-grained, uniform material called groundmass. Grain size in igneous rocks results from cooling time so porphyritic rocks are created when the magma has two distinct phases of cooling. [18]
Magma that is extruded as lava is extremely dry, but magma at depth and under great pressure can contain a dissolved water content in excess of 10%. Water is somewhat less soluble in low-silica magma than high-silica magma, so that at 1,100 °C and 0.5 GPa , a basaltic magma can dissolve 8% H 2 O while a granite pegmatite magma can dissolve 11% ...
[1] [39] It works on the temperature variation of the earth crust over time based on rate of heat transfer and diffusion along the disturbed geothermal gradient (normal heat distribution in the ground). [1] [2] Thermal modeling does not give the actual geological time. [1] However, it provides accurate estimation of the duration of the thermal ...
Magma exists in three main forms that vary in composition. [3] When magma crystallizes within the crust, it forms an extrusive igneous rock. Dependent on the composition of the magma, it may form either rhyolite, andesite, or basalt. [3] Volatiles, particularly water and carbon dioxide, significantly impact the behavior of each form of magma ...
[10]: 21 Water vapor plays an important role in lowering the melting point of silicic rock, [10]: 43 and some rhyolitic magmas may have a water content as high as 7–8 weight percent. [20] [21]: 44 High-silica rhyolite (HSR), with a silica content of 75 to 77·8% SiO 2, forms a distinctive subgroup within the rhyolites.
If water is cooled at a rate on the order of 10 6 K/s, the crystal nucleation can be avoided and water becomes a glass—that is, an amorphous (non-crystalline) solid. Its glass transition temperature is much colder and harder to determine, but studies estimate it at about 136 K (−137 °C; −215 °F). [ 9 ]