Chocolate!

The rock in the image appears to be a type of quartzite. Quartzite is a metamorphic rock that forms from the metamorphism of quartz sandstone. It's primarily composed of quartz grains that have been recrystallized under heat and pressure, giving it a hard, durable nature and often a somewhat glassy luster.
The colors and patterns you see, with light colors and darker veins, are typical of quartzite, which often retains some of the original sedimentary layering or banding from its sandstone precursor but in a more compact and crystalline form.
The presence of different shades like white, beige, and possibly some iron staining or other mineral inclusions could give it the varied coloration seen here.