So many talented people here ----->BethShape, I'm not sure how you'd go about doing marble on a small scale. Basically for that, I use an assortment of sponges and sponge rollers, overlaying different shades of whatever color I'm using, then paint in veins and texture with artist brushes and feathers, again using several colors so they look complex.
Tons of techniques on YouTube, I'd suggest checking that out.
I'm sending you a pm with some pics.