A mineral streak is a natural discoloration in wood that occurs when the tree absorbs and deposits minerals from the soil. These streaks appear as lines or bands that are typically black, grey, or olive in color and run parallel to the grain of the wood. While some carpenters may try to avoid mineral streaks, others find them to be unique and visually appealing. Mineral streaks are most commonly found in lighter woods like maple, cherry, hickory, and basswood, and they are especially noticeable when the wood is left unstained.