How do quartz veins form?
The formation of quartz veins needs fluids enriched in Si. Usually Si dissolves somewhere in neighbouring formations, gets transported by fluids and precipitates where the fluid pressure is low (the fluids Si-saturation capacity decreases with decreasing fluid pressure).
Fluid pressure is usually involved in rock fracturing. When it builts-up, it can fracture the rock. Thereby generated fractures, in turn, accomodate void space, hence the fluid pressure drops and Si precipitates from the fluid to form veins. These veins reseal and restrengthen the rock, which can again lead to a renewed fluid pressure built-up. This process is known as crack-seal vein formation.

Usually, crack-seal vein formation happens progressively, which is a very nice thing: Studying vein internal mineral structures gives evidence to past stress regime conditions. These evidences can help unraveling the evolution of tectonic structures, such as mountain formations or fault systems.

Quartz veins are very common, they need a source of disolvable Si, which is a really abundant element. In carbonate rocks, calcite veins are more common. The crack-seal principle applies for them just the same. 

Yes, you can see veins in satelite pictures! Have a look here: OMAN (These are calcite veins standing out against a darker limestone).

Hope this helps,
Ben

P.S.: You might want to have a look at my thesis on (calcite) vein-networks in Oman: LINK.