Chapter 03 Ans

Chapter 03 Ans - Answers for Chapter 3: Textures of Igneous...

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Answers for Chapter 3: Textures of Igneous Rocks. 1. Other than the externally-imposed cooling rate, what are the three principal rates that govern rock texture? Rates of nucleation, growth, and diffusion. 2. What is typically the determining (limiting) rate when large crystals form? Explain. Nucleation in this case is the limiting, or slowest, rate. Few nuclei form and crystal growth, and diffusion of components to the growing surfaces are sufficient to permit those few nuclei to grow into large crystals. 3. What is the determining rate when dendritic crystallization takes place? Explain. Diffusion is now the limiting rate and crystals extend to reach the limited supply of components that become depleted adjacent to the crystal surfaces as growth proceeds. 4. What is the distinction between primary textures and secondary textures? Primary textures take place between solids and liquid as the liquid solidifies (or remelts). Secondary textures affect existing solids without the participation of liquid. 5. Explain how porphyritic texture is most likely to develop. Although there are several ways, perhaps the most typical involves two stages of growth involving different cooling rates. The most common such occurrence involves phenocryst formation of early
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Chapter 03 Ans - Answers for Chapter 3: Textures of Igneous...

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