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Too tired to think

  • 08-10-2010 1:33am
    #1
    CrabieCrawford
    Registered Users, Registered Users 2 Posts: 642 ✭✭✭


    Three igneous rock samples (with no pores) contain three minerals, quartz, feldspar and mica. All
    samples have the same volume.
    The first sample has 50% feldspar, 30% pyroxene (a dark mineral) and 20% mica and weighs 2.72k.g.
    The second has 30% feldspar, 50% pyroxene and 20% mica and weighs 2.8kg.
    The third sample contains 30% feldspar, 70% pyroxene, and 0% quartz and weighs 2.78Kg
    If each sample was spherical and measured 5.0cm in diameter, what would be the density of each rock
    sample?

    I know its simple just cant get my head round it at this time of night, dont really need the answer, just how to do it. Worked out 1% values of each at feldspar = 0.025, pyroxene 0.029, and quartz at 0.03

    ie 50(0.025) + 30(0.029) + 20(0.03) = 2.72kg etc


Comments

  • #2
    gerry87
    Registered Users, Registered Users 2 Posts: 872 ✭✭✭gerry87


    First thought would be a simultaneous equation to find the weight for a 100% sphere of each rock. So F is a the wight of a 100% sphere of feldspar etc...

    .5*F + .3*P + .2*M = 2.72
    .3*F + .5*P + .2*M = 2.8
    .3*F + .7*P = 2.78

    then you know the volume of the sphere and the density is weight/volume.


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