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Name: Inarvis
Status: Educator
Age: 20s
Location: N/A
Country: N/A
Date: December 10, 2002


Question:
Hello! I am an Earth Science- student teacher. I have prepared an activity for my students in which they grow crystals of alum, salt and sugar at different temperatures (one sample is cooled at room temperature, the other in a fridge). The point is to demonstrate the effect of cooling temperature on crystal formation and relate this to the differences between extrusive and intrusive igneous rocks. I am designing an answer key to some questions, but I need your opinion on the answer to the following:

What are some important similarities and differences between this type of crystal formation (ie. in the lab, alum and sugar crystals) and the manner in which crystals in igneous rocks form?



Replies:
Alum, common table salt and sugar crystals are formed by the evaporation of water in a saturated aqueous solution of each. In contrast, igneous rock is formed by the crystallization of molten rock under high temperature and pressure. That is quite different.

Vince Calder



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