Native gold in quartz
The most common natural method of concentration of gold is through the ancient action of hot fluid inside the Earth's crust. (Fluids deep in the crust are heated by the Earth's internal heat. As they move towards the surface they cool down.)
The fluids moved through the rocks over a large area and "dissolved" the gold. When these fluids cooled or reacted with other rocks the dissolved gold precipitate (came out of the fluid) in cracks or fractures forming veins.
Among all the gold found on the Earth, nice visible veins of gold is rare. This piece is from Archean age ( about 2.6 billion years old) and comes from Western Australia. Has been only polished without adding any stabilizer. Is also visible a pyrite crystal.From California.