((
And where did all this sand come from? its dry so sand just pops up? and when theres no quartz sand yet sand is all over?
Where did the sand come from? How about the desert? If it winds towards that direction alone, it would seem pretty logical that the desert would start to expand 'downwards', towards the city.. Which it did. Strong wind can blow sand enormous distances you know. If the winds from south, west and east kept the desert from expanding, their sudden disappearance would cause the only remaining wind (northwind) to spread the sand. The desert *did* expand during the drought quest, and it spread the sand towards the city. I guess you failed to notice it while you were too busy being critical towards the quest in general. Your question has been answered. My first answer also answers to your second question directly, and the third one indirectly.
The quartz-sand did not disappear immediatly after the desert begun to spread. Before the quest, let's just assume that the upper-layers of the desert were quite full of quartz-sand, right? If you are still with me, observe: When the north-wind begun spreading the sand, the quartz-sand was blown away from the upper-sediments of the desert. Part of it was blown straight into the sea, where the rest landed on ground. There it got mixed with gravel, soil, dirt, grass and many other things constantly impurifying it. When most of the upper-sediments containing the quartz-sand had been blown away, the lower sediments with lesser-quality sand surfaced, and begun to spread over the already impure quartz-sand. This changed the impurity-levels so high, that most of it (quartz-sand) really wasn't useful anymore. The only places where quartz-sand can be discovered are the locations where the sediments of it reached deeper than in most of the desert.
Satisfied?))