When sourcing marble spheres, the primary concern is the geological origin and mineral composition. Buyers should request the specific type of marble (e.g., Carrara, Nero Marquina, or Calacatta) as this dictates the price and aesthetic. Ensure the product is natural stone rather than resin-based imitation by checking for natural vein patterns (which should not repeat) and thermal conductivity (natural marble feels cold to the touch). For high-end architectural or decorative use, verify the Mohs hardness scale rating to ensure durability against scratching.