Igneous rock texture Texture is anything that you can see in a rock that can give you clues as to how that rock formed. Vesicular texture is a volcanic rock texture characterized by a rock being pitted with many cavities (known as vesicles) at its surface and inside. Textures of Igneous Rocks The main factor that determines the texture of an igneous rock is the cooling rate (dT/dt) Other factors involved are: The diffusion rate - the rate at which atoms or molecules can move (diffuse) through the liquid. (You may also want to refer to Barker, 1983, pages 106-120; Hyndman, 1985, pages 49-61; or Jackson, 1970, pages 255-273. zIntergranular texture - a texture in which the angular interstices between plagioclase grains are occupied by grains of ferromagnesium minerals such as olivine, pyroxene, or iron titanium oxides. Magma Mixing and Mingling 10. Principal minerals are Potassium Feldspar, Biotite Mica, and Quartz. COARSE GRAINED TEXTURE , mineral grains easily visible (grains several mm in size or larger) A hand specimen of granite with phaneritic (coarse grained) texture. Texture - refers to degree of crystallinity, grain size, and geometrical relationships between the cons tituents of a rock (fabric). The rate of crystallization influences a lot in defining texture of igneous rocks. As magma rises to the surface the pressure on it decreases. GLG 333 -- IGNEOUS TEXTURES AND STRUCTURES The following is a reorganization and amplification of Blatt and Tracy, 1996, pages 39-44. This relates to the cooling history of the molten magma from which it came. This pile of igneous rocks contains a wide range of igneous rock compositions and textures and represents a dozen different rock names and histories. Igneous Rocks Igneous rocks are formed by the cooling of molten rock. Chapter 3: Igneous Textures The texture of a rock is a result of various processes that controlled the rock’s genesis and, along with mineralogy and chemical composition, provides information that we may use to interpret the rock’s origin and history Table 3.1 at end of Chapter 3 provides a glossary of common igneous rock textures . There are two major states of molten rock: Magma and Lava. Andesitic compositions are somewhere between basaltic and granitic in density, color and the explosive nature of an eruption. SUMMARY • Magma changes in temperature, viscosity, volatile content, and composition as it is transported toward the surface, mixes with other magmas, assimilates surrounding rock, and fractionates. Textures of Igneous Rocks Page 5 of 6 2/12/2004. Igneous rocks are classified according to their texture (coarse-grained vs. fine-grained) and their chemical and mineralogical compositions. Andesitic Intrusive Dike. 6.1.1. Following is a brief account of these textures of igneous rocks: I. Equigranular Textures: All those textures in which majority of constituent crystals of a rock are broadly equal in size are described as equigranular textures. Igneous Rocks: Texture and Composition. Mafic Complexes 9. The faster a rock cools down and solidifies, there is less time for crystallization to take place. How to Start a Speech - Duration: 8:47. Granitic Complexes 8. All igneous rock began as molten rock formed deep within the earth called magma. Texture describes the physical characteristics of the minerals, such as grain size. Texture is a very important means of determining the circumstances under which the rock was formed, and hence great attention is paid to it. There are six main types of textures; phaneritic, aphanitic, porphyritic, glassy, pyroclastic and pegmatitic. 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