At Piton Sainte Rose, Reunion Island, the basalt is rich in millimetre-sized crystals of' green olivine. Such lava is called picrite.
There are several possible origins for such rocks:
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The magma at the origin of this lava is a primitive magma resulting from a high rate of partial melting of the lherzolitic mantle.
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the primitive magma results from the partial melting of a more magnesian mantle than previously (e.g. harzburgitic).
In both cases, these magmas have undergone little or no magmatic differentiation.
- the third alternative is that the magma may have been enriched in olivine by a magmatic differentiation process.
When this basalt breaks down, the result is a sand enriched with olivine.
See the microscope photo under PPL and CPL?
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