Any of numerous minute rudimentary crystalline bodies of unknown composition found in glassy igneous rock

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
Crystallite \Crys"tal*lite\ (kr?s"tal-l?t), n. [See Crystal .] (Min.) A minute mineral form like those common in glassy volcanic rocks and some slags, not having a definite crystalline outline and not referable to any mineral species, but marking the first ...

Wiktionary Word definitions in Wiktionary
n. A small region of a solid that consists of a single crystal; a grain

WordNet Word definitions in WordNet
n. any of numerous minute rudimentary crystalline bodies of unknown composition found in glassy igneous rock

Wikipedia Word definitions in Wikipedia
Polycrystalline or multicrystalline materials, or polycrystals are solids that are composed of many crystallites of varying size and orientation. Crystallites are also referred to as grains . They are small or even microscopic crystals and form during the ...