crystallinity

geology

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June 17, 2026

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Crystallinity in geology refers to rocks composed entirely of crystallized minerals, without any glassy material. This is a fundamental property that provides insights into how a rock formed.12

Types of Crystallinity in Igneous Rocks:

Holocrystalline: Entirely crystalline.2
Hemicrystalline/Hypocrystalline: Contains crystalline material and some glass.2
Hemi-hyaline/Hypohyaline: Primarily glass with some crystalline material.2
Holohyaline/Hyaline: Entirely glassy.2

The rate of cooling significantly influences crystallinity. Slow cooling, typical of rocks formed deep within the Earth, allows for the growth of larger crystals, resulting in phaneritic (coarse-grained) textures. Rapid cooling, common in volcanic rocks, leads to aphanitic (fine-grained) or glassy textures. Metamorphic rocks are almost always crystalline.21

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igneous rock
Crystallinity
Among the most fundamental properties of igneous rocks are crystallinity and granularity, two terms that closely reflect differences in magma composition and the differences between volcanic and various plutonic environments of formation. Crystallinity generally is described in terms of the four categories shown in…
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Among the most fundamental properties of igneous rocks are crystallinity and granularity, two terms that closely reflect differences in magma composition and the differences between volcanic and various plutonic environments of formation. Crystallinity generally is described in terms of the four categories shown in…
Read More

sedimentary rock
Origin of banded iron formation
The essentially crystalline texture of these minerals together with the definitive crystalline texture of the laminated chert bands with which the iron mineral layers alternate is perplexing. At present, iron is not easily dissolved, nor can it be readily transported in solution and subsequently precipitated as crystalline-textured,…
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The essentially crystalline texture of these minerals together with the definitive crystalline texture of the laminated chert bands with which the iron mineral layers alternate is perplexing. At present, iron is not easily dissolved, nor can it be readily transported in solution and subsequently precipitated as crystalline-textured,…
Read More