This is guaranteed to be a genuine Cook Islands Black Pearl.
The price of a pearl depends on its quality and size. Pearls are graded by size, shape, surface characteristics, color and lustre. Size is in millimetres ranging between 8 and 12 with the occasional rare beauty reaching 13 to 15 millimetres. Surface characteristics can include surface blemishes such as pits, bumps, ridges, cracks and spots.
Color is a matter of taste: it can range from deep black through silver grey and into white. Lustre is caused by the reflection of light from the surface. Shape can be classified by round, drop or pear, button (round one side and flat the other), baroque (irregular) and circled (ringed).