Waxy!

This rock has a distinctive yellowish-orange to brownish color with a glossy, polished appearance and some white or light-colored inclusions or streaks. It also has a somewhat porous or pitted texture in places, with darker brown or black lines running through it. Here’s my analysis of what this rock might be, considering the context of Lucky Peak Reservoir near Boise, Idaho:
Petrified Wood: This remains a strong possibility, especially given the organic, wood-like patterns and the color palette (yellowish-orange to brown). Petrified wood forms when wood is buried and replaced by minerals like silica (quartz), often resulting in a hard, stone-like material with preserved grain patterns. The lighter areas could be quartz or calcite infill, and the darker lines might represent the original wood structure or mineral veins. The glossy, polished surface suggests it’s been tumbled or treated, which is common for petrified wood specimens. Idaho, including areas near Boise, has deposits of petrified wood, particularly in volcanic or sedimentary regions, which aligns with the geology around Lucky Peak.
Agate or Jasper: These are forms of chalcedony (quartz) that can have similar colors and polished appearances. Agate often has banding or translucent areas, while jasper is typically opaque and earthy, like the colors in your rock. The yellowish and brownish tones, along with the glossy sheen, could indicate agate, especially if there’s any translucence (you’d need to check in strong light). However, the porous or pitted texture and darker lines might lean more toward jasper or a mix of silicified material. Both agate and jasper are found in Idaho’s volcanic and sedimentary deposits.
Opal or Common Opal: The yellowish-orange color and glossy appearance could suggest a form of opal, particularly common opal (non-gem-quality opal without the play-of-color of precious opal). Common opal can have earthy tones and a waxy or glassy luster, and it can occur in volcanic or sedimentary settings. The white inclusions might be silica or other minerals, and the pitting could indicate weathering or natural voids. Idaho has opal deposits, though they’re more common in areas like the Owyhee Mountains, not necessarily right at Lucky Peak.
Chert or Flint: These are microcrystalline quartz varieties that can have similar colors and textures. Chert often appears in nodules or layers and can be porous or pitted, matching the appearance of your rock. It’s found in sedimentary deposits, which are present in the Boise area, but the vibrant colors and glossy finish make this less likely than petrified wood or agate.
The geology around Lucky Peak Reservoir includes volcanic rocks, sedimentary deposits from the Boise River, and metamorphic rocks from the Idaho Batholith. The Boise River and its tributaries could carry such rocks downstream, and tumbling in the river or polishing could explain the smoothed, glossy look. The color and texture suggest a silicified or mineralized material, likely from a natural process involving wood or silica-rich deposits.
To narrow it down further, consider:
The rock’s hardness (petrified wood, agate, jasper, and opal are around 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 petrified wood, agate, or opal, all of which occur in Idaho.
Its weight and density—petrified wood and agate feel heavier due to mineral replacement, while opal might feel lighter.
Whether it shows any translucence or play-of-color (indicative of opal, though unlikely here).
Given the context and appearance, I’d lean toward petrified wood or agate, both of which are plausible for the Boise area. Petrified wood seems more likely if the patterns resemble wood grain or organic structures, while agate fits if it has subtle banding or a more uniform, glassy look.