文档介绍：岩石学-岩石学2-火成岩的结构与构造
玻璃质是岩浆快速冷却结晶的，其中原子的排列处于完全无序的状态，具很高的自由能，因此玻璃质是一种十分不稳定的固态物质，随着地质时代的增长和/或挥发组分、温度和压力的参与，将逐渐转变为稳定态的结晶质，分。前者指条纹长石中钾长石为主晶而钠长石为含量低的客晶呈条纹分布于钾长石之中。反之，则称为反条纹结构。条纹结构是矿物结晶后，又发生了固溶体分离所形成。这类条纹具定向性，常沿主晶的某一结晶学方向均匀分布，条纹的形态及分布比较规则。也有一些条纹为交代成因，条纹常常较主晶新鲜，多呈不规则的树枝状、网脉状，定向性不明显，常顺主晶的裂隙、解理、边缘等处分布。
文象结构（Graphic texture):石英呈一定的外形（如尖棱形，象形文字形等）有规律地镶嵌在钾长石中，这些石英在正交偏光下同时消光。肉眼可见的叫文象结构，镜下才能见到的叫显微文象结构。基质具显微文象结构的斑状结构称花斑结构。文象结构是长石和石英在共结点同时结晶形成的。
5: Igneous Textures
Idealized rates of crystal nucleation and growth as a function of temperature below the melting point. Slow cooling results in only minor undercooling (Ta), so that rapid growth and slow nucleation produce fewer coarse-grained crystals. Rapid cooling permits more undercooling (Tb), so that slower growth and rapid nucleation produce many fine-grained crystals. Very rapid cooling involves little if any nucleation or growth (Tc) producing a glass.
Igneous Textures
Backscattered electron image of quenched “blue glassy pahoehoe,” 2019 Kalapana flow, Hawaii. Black minerals are felsic plagioclase and gray ones are mafics. a. Large embayed olivine phenocryst with smaller plagioclase laths and clusters of feathery augite nucleating on plagioclase. Magnification ca. 400X. b. ca. 2000X magnification of feathery quenched augite crystals nucleating on plagioclase (black) and growing in a dendritic form outward. Augite nucleates on plagioclase rather than pre-existing augite phenocrysts, perhaps due to local enrichment in mafic components as plagioclase depletes the adjacent liquid in Ca, Al, and Si. © John Winter and Prentice Hall.
Igneous Textures
a. Volume of liquid (green) available to an edge or corner of a crystal is greater than for a side. b. Volume of liquid available to the narrow end of a slender crystal is even greater. After Shelley (1993). Igneous and Metamorphic Rocks Under the Microscope. © Chapman and Hall. London.
b
a
Igneous Textures
a. Skeletal olivine phenocryst with rapid grow