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TEXTURES OF IGNEOUS ROCKS
- 1. INTERGROWTH & IN-EQUIGRANULAR WRITTEN BY: MU H A MMA D S O H A I B ( F A 18 - GEO - 006 )
- 2. CONTENT INTERGROWTH Graphic Texture Perthite Texture Myrmekite Texture Granophyric Texture IN-EQUIGRANULAR Porphyritic Texture Poikilitic Texture Ophitic Texture Vitrophyric Texture
- 3. INTERGROWTH
- 4. GRAPHIC TEXTURE A graphic texture is an igneous rock texture in which an intergrowth of two minerals has the appearance of runic writing. • Granophyric: Rocks with abundant graphic texture • They are intergrowths of quartz and alkali feldspar in which the quartz appears as v-shaped inclusions enclosed by the feldspar. • It can only observed under the microscope. • They originate by simultaneous crystallization of phases from a silicate melt in the presence of a hydrous fluid phase.
- 6. THIN SECTION
- 7. PERTHITE TEXTURE A perthite is an intimate intergrowth of sodic and potassic feldspar resulting from subsolid exsolution (unmixing of two minerals). • Named after the nearby city of Perth in Ontario. • The term perthite is often used to describe all types of exsolution in the feldspars. • The other division of this sub-group include: 1. Anti perthite 2. Meso perthite 3. Micro perthite
- 9. THIN SECTION
- 10. MYRMEKITE TEXTURE Myrmekite is an intergrowth of branching rods of quartz set in a single crystal of plagioclase. • Derived from the ancient greek "myrmekia" (wart) and was used by Jakob Cederholm in 1899 for the first time to describe these structures. • Also, neighboring rod of quartz have the same lattice orientation and extinguish together. • There is a lot discussion on this texture but the most accepted hypothesis goes back to Becke (1908) who proposed the reaction of na- and ca-bearing fluids with k-feldspar. KAlSi3o8 + Na+ = NaAlSi3O8 + K+ 2KAlSi3O8 + Ca2+ = CaA𝑙2Si2 𝑂8 + 4SiO2 + 2K+
- 11. THIN SECTION
- 12. THIN SECTION
- 13. GRANOPHYRIC TEXTURE A granophyric texture is an intergrowth of quartz and alkali feldspar in an igneous rock that is less well defined than a graphic texture and often is somewhat radiating. • These textures document simultaneous crystallization of quartz and feldspar from a silicate melt at the eutectic point, perhaps in the presence of a water-rich phase. • They may also be formed by crystallization when the magma is significantly undercooled, not necessarily under eutectic conditions.
- 14. PETRO SECTION
- 15. THIN SECTION
- 16. IN-EQUIGRANULAR
- 17. PORPHYRITIC TEXTURE Porphyritic texture is an igneous rock texture in which large crystals are set in a finer-grained or glassy groundmass. • Porphyritic textures occur in coarse, medium and fine-grained igneous rocks • The larger crystals, known as phenocrysts, formed earlier in the crystallization sequence of the magma • A porphyritic texture in which there is a continuous variation in crystal size is termed seriate. • Hypabyssal rocks with porphyritic textures are sometimes termed porphyry.
- 18. PORPHYRITIC TEXTURE Porphyritic texture is divided into four types on the basis of ground mass. 1. Granular porphyritic: Ground mass consists of fine crystals less than 1mm. 2. Micro-porphyritic: Ground mass consists of micro-crystals. 3. Felsophyric: Ground mass consists of cryptocrystalline materials. 4. Vitrophyric: Ground mass is glassy.
- 19. PETRO SECTION
- 20. THIN SECTION
- 21. POIKILITIC TEXTURE Poikilitic texture refers to crystals, typically phenocrysts, in an igneous rock which contain small grains of other minerals. • In many poikilitic texture the enclosed crystals are randomly arranged, in other may be concentrated in zone and in some case crystals have a specific crystallographic relationship to the host. • One of the best known is the arrangement of plagioclase and mica enclosed in k-feldspar.
- 22. POIKILITIC TEXTURE “Mc Birney and Noyes (1979) show that this texture may be originated as a result of differing nucleation and growth rates, so that a single crystal (like pyroxene) nucleate and growth to a large size (low nucleation rate) in contrast to several other minerals (like feldspars) with higher nucleation rate which necessarily remain relatively small and became successively entrapped in the pyroxene.”
- 23. PETRO SECTION
- 24. THIN SECTION
- 25. OPHITIC TEXTURE Ophitic texture, a variant the poikilitic texture, is one where random plagioclase laths are enclosed by pyroxene or olivine. • This textural sequence is typically found at the margins toward the center in diabasic or doleritic rocks (basaltic dikes) or from the chilled surface to depth of basaltic flows • If plagioclase is larger and encloses the ferromagnesian minerals, then the texture is sub ophitic and the laths typically impinge on one another to form sharp angles.
- 26. OPHITIC TEXTURE • Note that the change from intergranular through sub ophitic to ophitic textures in basaltic rocks results from slower cooling and slower nucleation rates. • If the cooling rate is very fast, the interstitial material between plagioclase laths may be quenched to glass to form an intersertal texture.
- 27. PETRO SECTION
- 28. THIN SECTION
- 29. VITROPHYRIC TEXTURE Vitrophyric / Vitriomorphic is variety of inequigranular porphyritic texture in which larger crystals known as phenocrysts are embedded in a glassy ground mass. • Glassy and Vitrophyric texture occur in volcanic rocks. • These are composed of disintegrated fragments of glass, rocks, minerals, or pumice cemented by volcanic ash. • Presence of glass among pyro clasts defines the hyaloclastic texture.
- 30. PETRO SECTION
- 31. THIN SECTION
- 32. BIBLIOGRAPHY
- 33. I have use https://www.alexstrekeisen.it/English for much of my content, also take some of the details from SlideShare https://www.slideshare.net/AhmedEssam240/igneous-rock-textures-78370809 and least from other resources.