Xenocrysts

Part of speech: noun

Definitions

1. Fragments of foreign minerals that are found within an igneous rock, indicating the presence of different geological environments
2. crystals originating from parent rocks that differ in composition from the surrounding matrix
3. distinct mineral inclusions that provide insights into the geological history and formation processes of the host rock

Etymology: "Xenocrysts" is the plural of "xenocryst", a crystal that was formed in one rock and later carried into another, so it is foreign to the rock that contains it. The word is built from two Greek-derived parts. "Xeno-" comes from Greek "xenos", meaning "stranger" or "foreign", the same element found in "xenophobia". "-cryst" comes from Greek "krystallos", meaning "ice" or "rock crystal", which gave English "crystal". The pairing is a clear description of what the mineral is: a stranger crystal. Geologists picked the prefix because the crystal did not grow in the host rock alongside its neighbours. It was picked up from elsewhere, such as fragments of older rock swept up by magma on its way to the surface, and its composition and age can reveal where the magma has been.