Answer to Question 1
Answer: The structure depends on the temperature and moisture conditions that exist when the crystal is formed. If all of a crystal's growth occurs under similar conditions, its structure can be quite simple. If, on the other hand, the temperature and moisture conditions change during growth, a complex mixture of plate, needle, and dendrite can develop.
Answer to Question 2
Answer: Any three of the following: dendrites, plates, columns, needles, or complex mixtures.