Rare Double Opal Pineapple
Gold [ Au ] over Quartz [ SiO2 ]
Gold in its natural mineral form almost always has traces of silver, and may also contain traces of copper and iron. A Gold nugget is usually 70 to 95 percent gold, and the remainder mostly silver. The colour of pure Gold is bright golden yellow, but the greater the silver content, the whiter its colour is.
Much of the gold mined is actually from gold ore rather then actual Gold specimens. The ore is often brown, iron-stained rock or massive white Quartz, and usually contains only minute traces of gold. To extract the gold, the ore is crushed, then the gold is separated from the ore by various methods.
[ Excerpt from Minerals.net ]
Gold over Quartz