GEOL 21062 Lecture Notes - Lecture 19: Flow Chemistry, Dacite, Chemical Classification
31 Jan 2020
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Show picture of an explosive volcanic eruption and ask why are some fun to watch whereas for others it is better to be far away. Lava => molten rock on the earth surfaces. Explosive: pyroclastic classification dependent on fragment content and size. Classified based on texture and - importantly - chemistry, which in the field is more or less determined by color. Chemical classification of volcanic rocks (explain that this is based only on chemistry) Melts have internal structure (but no long-range order like crystals) Similar to minerals, a silicate melt structure is formed by sio4 tetrahedra and, depending on composition, these tetrahedra form specific networks. So for the melt structure we distinguish network formers (si4+, al3+, fe3+) and network modifiers (na+,k+,ca2+, oh-) Draw a picture of the network including network modifiers etc. The longer range the network is, the higher the viscosity (if t, volatiles etc are all the same)
