Crystallinity

In geochemistry, mineral crystallinity plays a pivotal role in regulating water-rock interactions, particularly during the early stages of mineral crystallization. For example, in the case of goethite, dissolved lithium can be taken up by poorly crystallized goethite, whereas little sorption occurs in well-crystallized goethite. Additionally, lithium isotope fractionation during low-temperature water-rock interactions is controlled by reactions occurring at defect sites in poorly crystallized minerals, such as hectorite and goethite. == Rock crystallinity ==

Geologists describe four qualitative levels of crystallinity: • holocrystalline rocks are completely crystalline; • hypocrystalline rocks are partially crystalline, with crystals embedded in an amorphous or glassy matrix; • hypohyaline rocks are partially glassy; • holohyaline rocks (such as obsidian) are completely glassy. ==References==