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    IS it really molten rock and how hot does a rock have to become to melt can everything melt???

    just wondering randomly lol x
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    anything can melt.
    iirc its not so much to do with temperature its about pressure
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    Yes, it is - or more, can be - a lot of lava is porphyritic in nature, hence it contains phenocrysts during eruption (crystals which have formed prior to eruption - coincidentally prior to its extrusion lava is called magma).

    A lava can vary in composition, this is usually measured in terms of the weight percent of the rock composed of Silica (Si) - lava extruded onto the earths surface rarely has a composition of less than 48% and greater than 75% Si. The lower the weight percent of Si, the lower the viscosity of the material and the higher the temperature required to extrude. The inverse of these conditions is seen with higher Si values - this can be explained because of the low melting point of Quartz (SiO2) and the high inclusion of volatile gases within quartz bearing minerals, which cause the greater viscosity.

    The "melting temperature" of lava is difficult to define due to it containing a variety of minerals. Because of this, phase diagrams showing variation with temperature show a phase where the material is "semi molten" between the solidus and liquidus lines.

    The hottest lavas commonly extruded in the modern day are on hawaii, and can be upwards of 1300C (where the Si% of lava is approximately 47%).
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    (Original post by dh00001)
    anything can melt.
    iirc its not so much to do with temperature its about pressure
    Carbon dioxide only rarely melts, as does iodine.

    The temperature-pressure relationship is very important with volcanism (mid ocean ridge magmas form through adiabatic decompression, hence the pressure change causes the melting). Although, most common cause of magma generation is water - when it's subducted with oceanic slabs its presence lowers the solidus of a rock and dehydration reactions cause melting in the slab and mantle.
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    (Original post by bikerx23)
    Yes, it is - or more, can be - a lot of lava is porphyritic in nature, hence it contains phenocrysts during eruption (crystals which have formed prior to eruption - coincidentally prior to its extrusion lava is called magma).

    A lava can vary in composition, this is usually measured in terms of the weight percent of the rock composed of Silica (Si) - lava extruded onto the earths surface rarely has a composition of less than 48% and greater than 75% Si. The lower the weight percent of Si, the lower the viscosity of the material and the higher the temperature required to extrude. The inverse of these conditions is seen with higher Si values - this can be explained because of the low melting point of Quartz (SiO2) and the high inclusion of volatile gases within quartz bearing minerals, which cause the greater viscosity.

    The "melting temperature" of lava is difficult to define due to it containing a variety of minerals. Because of this, phase diagrams showing variation with temperature show a phase where the material is "semi molten" between the solidus and liquidus lines.

    The hottest lavas commonly extruded in the modern day are on hawaii, and can be upwards of 1300C (where the Si% of lava is approximately 47%).

    WOAH WHO R U A LECTURERE??

    thanks anyhooo
    xxxxxxxxxx
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    (Original post by ladymoon)
    WOAH WHO R U A LECTURERE??

    thanks anyhooo
    xxxxxxxxxx
    Nah - I did a geology degree specialising in volcanology for my Masters.

    And, any time.
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    (Original post by bikerx23)
    Nah - I did a geology degree specialising in volcanology for my Masters.

    And, any time.

    wow i asked in the right place so whats the silica part bit mean again does that affect the melting point or what??
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    (Original post by ladymoon)
    wow i asked in the right place so whats the silica part bit mean again does that affect the melting point or what??
    It's the main indicator of the lava's composition, yes - it is very useful as it is indicative of many aspects of the lava's behaviour - as said, it directly influences both the melting temperatures, viscosity and volatile content, which are significant factors in the method of eruption (massive explosive volcanoes require high volatile contents.etc.)
 
 
 
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