University:
Massachusetts Institute of Technology
Course:
12.109 | Petrology
Academic year:

2021
Views:

147

Pages:

14
Author:

rezancuk2j

Non-crystalline Igneous Texture Non-crystalline Texture Glassy Glass-like texture resulting from near-instant solidification of melt, preventing the formation of mineral crystal structure. Has microlites and cryptocrystalline minerals. Non-crystalline Texture Glassy Quenching occur when melt is in contact with liquid water or air. Rapid Loss of Dissolved Gas is limited to silicic melts; why obsidian is more common than basaltic glass Non-crystalline Texture Glassy Vitrophyric Texture has recognizable phenocryst in glassy groundmass. Spherulitic Texture has crystals growing outward from existing crystal nuclei Non-crystalline Texture Glassy Devitrification occurs when glass crystallizes on pre-existing microlites or cryptocrystalline nuclei. Perlitic Texture has cloudy appearance and curved cooling cracks. Non-crystalline Texture Vesicular Has spherical or ellipsoidal void spaces due to exsolution and entrapment of gas bubbles in lava. Vesicular rock name if > 30% vesicles by volume Vesicular + rock if 5% - 30% vesicles Vesicular-bearing + rock if < 5% vesicles Non-crystalline Texture Pyroclastic Fragmented particles of various sizes from volcanic eruptions. Classified based on Composition, Size, & Shape Non-crystalline Texture Pyroclastic Based on Composition: Lithic Pyroclasts are rock fragments Vitric Pyroclasts are glassy fragments Crystals Pyroclasts are minerals Non-crystalline Texture Pyroclastic Based on Shape and Sizes: Blocks/Bombs if > 64mm pyroclasts Lapilli if 2mm – 64 mm pyroclasts Ash if < 2mm pyroclasts Dust if < 0.0625 mm pyroclasts; Fine Ash Non-crystalline Texture Pyroclastic Welding Fragments become progressively fused together as porosity decreases during compaction, resulting to elongated, flat, parallel fragments. Non-crystalline Texture Glassy Vitrophyric Non-crystalline Texture Spherulitic Perlitic Non-crystalline Texture Scoria Pumice Non-crystalline Texture Pyroclastics Welded pyroclastics

Textures of Igneous Rocks Lecture Part 4

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