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For example, if there were a large land area with exposed basalt, in the middle of which is a smaller isolated patch of Granite, what is that isolated patch called?

I came across the single-word geological term for this some months ago, and now it eludes me.

Something tells me it had a similar ring to Moraine (as in glacial debris), but I may well be misremembering that connection.

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  • $\begingroup$ Xenolith usually applies to smaller fragment within an igneous rock - from Greek it means stranger stone. If the granite punched its way through the basalt, after the basalt had solidified it could be called an intrusion. $\endgroup$ – Fred Feb 26 at 18:12
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You might want to look at these topics, depends on the size of features that you want to look at:

  1. Batholith -- s a large mass of intrusive igneous rock (also called plutonic rock), larger than 100 square kilometres (40 sq mi) in area,[1] that forms from cooled magma deep in the Earth's crust. Batholiths are almost always made mostly of felsic or intermediate rock types, such as granite, quartz monzonite, or diorite -- https://en.wikipedia.org/wiki/Batholith
  2. Stock (geology) == is an igneous intrusion that has a surface exposure of less than 100 square kilometres (40 sq mi),[differing from batholiths only in being smaller. A stock has a discordant relationship with the rocks that it intrudes. The term stock usually refers to individual, relatively small plutons, less than 20 km (12 mi) diameter, usually in relative isolation.Many stocks are cupolas of hidden batholiths. Circular or elliptical stocks may have been vents feeding former volcanoes -- https://en.wikipedia.org/wiki/Stock_(geology)
  3. Dike (geology) -- is a sheet of rock that is formed in a fracture in a pre-existing rock body. Dikes can be either magmatic or sedimentary in origin. Magmatic dikes form when magma flows into a crack then solidifies as a sheet intrusion, either cutting across layers of rock or through a contiguous mass of rock. Clastic dikes are formed when sediment fills a pre-existing cracks -- https://en.wikipedia.org/wiki/Dike_(geology)
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