Quartzite!

This rock has a smooth, polished appearance with a mix of white, gray, and brownish-orange colors, featuring swirling, banded patterns. It also has a glossy, waxy sheen, suggesting it might have been naturally tumbled or polished. Here’s my analysis of what this rock might be, considering the context of Lucky Peak Reservoir near Boise, Idaho:
Agate: This is the most likely candidate. Agate is a variety of chalcedony (a form of quartz) known for its banded or layered patterns, often in shades of white, gray, and brown, with occasional iron oxide staining (like the orange-brown hues here). The smooth, polished surface and translucent or semi-translucent quality (if viewed in strong light) are characteristic of agate. Agate forms in volcanic or sedimentary rocks, typically in cavities or vesicles, and is common in Idaho, including areas with volcanic activity like those near Boise and Lucky Peak.
Jasper: Another possibility is jasper, which is also a form of chalcedony but is usually opaque and has more earthy, uniform colors. The brownish-orange streaks could indicate jasper, especially if it’s mixed with or stained by iron oxides. However, the banded, swirling patterns and glossy finish lean more toward agate than typical jasper, which tends to be less patterned and more solid in appearance.
Chalcedony: More broadly, this could simply be a piece of chalcedony, the broader category that includes agate and jasper. Chalcedony can have similar colors and textures, forming in similar geological environments. The white and gray areas might be purer silica, while the brown-orange is likely iron oxide or manganese staining.
Petrified Wood (Less Likely): While petrified wood was a possibility in your earlier images, this rock lacks the clear wood grain or organic patterns typically seen in petrified wood. However, if the banding mimics wood grain, it could be a highly silicified piece of petrified wood, but this is less probable given the uniformity and lack of visible woody structure.
The geology around Lucky Peak Reservoir includes volcanic rocks (like rhyolite and basalt), sedimentary deposits from the Boise River, and metamorphic rocks from the Idaho Batholith. Agate and chalcedony often form in volcanic rock cavities or as nodules in sedimentary layers, and the Boise River could have carried and tumbled such rocks, resulting in the smooth, polished appearance. The brownish-orange coloration likely comes from iron oxide staining, which is common in Idaho’s geological formations.
To narrow it down further, consider:
The rock’s hardness (agate and chalcedony are around 6.5-7 on the Mohs scale—scratch it with a knife or steel to test).
Where it was found—near Lucky Peak or the Boise River would support agate or chalcedony, both of which occur in Idaho.
Its translucence—hold it up to strong light to see if it’s translucent (more likely agate) or opaque (more likely jasper).
Its weight and density—agate feels heavier due to its silica content.
Given the context and appearance, I’d lean strongly toward agate, as the banded patterns, colors, and polished surface are classic indicators of this material. It’s a common find in Idaho, especially in areas with volcanic or riverine activity like those near Boise.