Colloids and Xenoliths

Xenoliths are inclusions of foreign material in a formerly-fluid rock mass.  In the following a distinctive property of the xenoliths in crystalline rock, namely their resistance to dissolving away.

Grimsel region, Switzerland

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Bernina region, Switzerland 

Bergell, Switzerland
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Bergell, Switzerland
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Bergell, Switzerland (Bergeller Intrusion), where later crystals have formed within the xenoliths.
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 Location not known 
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Quarz-Xenolith
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At first the xenoliths do not seem to hold anything puzzling.  the majority of the fine-grained objects with high biotite content (biotite = black mica) are inclusions within granodiorite or other rocks from deeper regions, whose melting temperature lay above that of the surrounding fluid material.  They were broken off from an already-hardened zone and carried away by the hot, fluid magma.  The last picture could appear puzzling, since, due to the lower melting point of the quartz, would require a different explanation.

Since numerous small objects preserved themselves over very long time periods in the still-fluid granite complexes without being dissolved, the question can also arise here, whether the consistency of the original mass was something other than hot-magmatic.

The pictures below show how, with experiments involving colloids, small broken-off pieces arise, which swim away from their place of origin and naturally show no signs of dissolving.

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Since numerous, often quite small inclusions have not dissolved in foreign fluid masses, one can conjecture that differing melting temperatures were not always the reason, but rather that a colloidal consistency may have played a role.