holocrystalline

Holocrystalline is a texture term in geology and petrology describing igneous rocks in which the entire rock is composed of interlocking crystals, with no glassy or vitreous material present. The crystals may be large enough to see with the naked eye or too small to discern without magnification; rocks with visible crystals are described as macrocrystalline or phanerocrystalline, while crystals too small to discern are microcrystalline or cryptocrystalline.

The term is used to distinguish rocks that crystallized completely from those that contain a glassy phase. Holocrystalline rocks arise when crystallization occurs throughout the molten mass, though crystal size reflects cooling rate and composition. In petrographic practice, many plutonic rocks such as granite, diorite, and gabbro are holocrystalline; some volcanic rocks that crystallize without a glassy groundmass are also described as holocrystalline.

Contrast with hypocrystalline textures, which contain both crystalline components and a glassy or vitreous groundmass. Microcrystalline and cryptocrystalline terms describe rocks whose crystals are too small to be seen without a microscope, and such textures can be holocrystalline as well.

Etymology: from holo- meaning whole, and crystallinus meaning crystalline. The term is standard in petrology for describing the purity of crystallinity in igneous rocks and helps distinguish fully crystalline rocks from glassy or partly crystalline varieties.