Found in various places in Idaho, including Owyhee County, petrified wood allows rockhounds to learn about the area's ancient climates by determining the types of trees that once grew there. The colors in Spencer Opal make it one of the world's most popular opals. Spencer Opal is mined in eastern Idaho, near Spencer, Idaho. Opals contain water, which eventually evaporates, damaging the opal. Nearly all surface rocks contain quartz, but Smoky Quartz is found only in certain areas, like Idaho's Sawtooth Mountains.
Smoky quartz is yellow to dark brown or black.