1) Not all white quartz will contain gold lines. 2) Gold is also found in non-rusty quartz. 3) Some thicker (cruder) gold lines will be iron pyrite. The reason we do the scratch test is to determine if we have located gold of golden colored pyrite. Gold will dent and is soft. Anything else that is not a valuable will crumble. There is an outside chance you could find platinum which is silver grey in color.
The single most common gold-bearing matrix in the world as a whole is the quartz vein.I'm no geologist, but as a hard-rock or placer gold miner I do know that having a basic understanding of the geological characteristics of auriferous quartz veins is important.