The small round seeds of various mustard plants are mustard seeds. The seeds typically have a diameter of around 1 to 2 millimetres (0.039 to 0.079 in) and can be coloured from yellowish white to black. As they are filled with a mineral called selenium, which makes your bones stronger, mustard seeds are good for your bones. They also help your nails, hair, and teeth to strengthen. There are antioxidant and anti-inflammatory properties in mustard seeds that help relieve pain in the gums, bones , and teeth.