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An inclusion in an igneous rock which is not genetically related, such as an unmelted fragment of country rock. Also known as accidental inclusion; exogenous inclusion.



a rock fragment that is foreign to the igneous rock in which it occurs. If the igneous rock enclosing the xenolith solidified at a great depth, then the xenoliths are usually greatly altered fragments of those rocks into which the magma intruded. But if the xenoliths are enclosed in the lava of a volcano, then they are usually fragments from the walls of the volcanic vent. The dimensions of the xenoliths vary greatly; they may be as small as individual crystals and their fragments, which can be distinguished only under a microscope (xenocrysts), or as large as several dozens or hundreds of meters.

References in periodicals archive ?
Pellet-rich tuffistic (volcaniclastic) serpentine kimberlite breccia occupies the southern fissure appendage of the pipe which is extremely rich in mantle xenocrysts, megacrysts and xenoliths.
Xenoliths are rock fragments or inclusions that are torn from the sides of lava tubes and caught up in magma as it moves through Earth.
Kaersutite and pargasite are amphiboles typical of alkaline basic rocks and metasomatised mantle xenoliths and their formation occurs early during the crystallization process (e.
6), with block structure comprising numerous xenoliths (up to ~100 m long) of pervasively recrystallised Unity anorthosite hosted by igneous-textured leucogabbronorite-leuconorite (Fig.
Research eventually established that diamonds come from the included bodies in kimberlite, not from the groundmass; that these bodies are xenoliths, not phenocrysts; and that the xenoliths (and, therefore, the diamonds) are much older than the kimberlite which carried them to the surface.
Hill and Ross (1983) concluded that the age of 238 [+ or -] 26 Ma obtained from a granulite xenolith represented the cooling age of the dyke, and is in close agreement with the 246 [+ or -] 4.
Some of them entrain deep crustal and mantle xenoliths to the surface, providing the only direct rock samples of the lithosphere available to us.
Albite occurs abundantly in fractures and as drusy coatings on altered granitic xenoliths in the Coal Hill vein.
The nature of the subcontinental lithospheric mantle (SCLM) of the Slave is particularly well defined through geophysical and xenolith data.