GY111 Earth Materials Laboratory Exercise 2 Igneous Rocks Igneous Rocks Problem Set Problem 1 Define the following terms 1 Aphanitic 2 Phaneritic 3 Porphyritic 4 Phenocryst 5 Groundmass Problem 2 In the space below describe how a Basalt porphyry would form from a magma Assume that the phenocrysts are Ca Plagioclase crystals You may use a sketch to help illustrate your answer Page 1 of 3 GY111 Earth Materials Laboratory Exercise 2 Igneous Rocks Problem 3 Define the following terms 1 Scoria 2 Pumice 3 Vesicles 4 Obsidian 5 Tuff Problem 4 Why do pegmatites form such large crystals Page 2 of 3 GY111 Earth Materials Laboratory Exercise 2 Igneous Rocks Problem 5 You may have noticed that the igneous rock samples that we use for lab lacks any examples of ultramafic extrusive volcanic rocks termed Komatiites Komatiites are rarely found on Earth and are always very old dating back to Precambrian time 540 Ma Why don t Komatiites form now What must have been different about Earth back in Precambrian time Problem 6 During the crystallization of a large magma chamber at great depth i e slow cooling assume that Bowen s Reaction Series controls the order of crystallization of silicate minerals In the below diagram fill in the expected composition and mineral content of each layer assuming that as each crystal formed it settles to the bottom of the chamber forming a layered intrusion i e fractional crystallization Page 3 of 3
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