Abalone vs Mother of Pearl

Abalone is a gastropod shellfish which has an ear-shaped shell. Mother-of-pearl is iridescent inner layer of mollusk shell. This iridescent layer is also produced from the shell of abalone. Therefore, the key difference between abalone and mother-of-pearl is that abalone is an organism, and mother-of-pearl is the inner layer produced from the shell of this organism.

Abalones are marine shells, It is a shellfish which has only one shell instead of two closely connected shells. Abalone shell can be used to make jewelry and other decorative ornaments.
Mother of pearl is also called nacre, a durable, glittering inner layer that can be found inside the shell of many mollusks. It is created from not only abalone, but also pearl oysters and freshwater pearl mussels. It is iridescent, strong. Used for the making of jewellery, elements in musical instruments, decorate watches and are sometimes embedded in to furniture. Mother of pearl is tinted artificially to any colour and cut into different shapes.

Definition:
Abalone is a type of Gastropod shellfish.
Mother of Pearl is the pearly internal layer found in some mollusk shells.

Saltwater vs Freshwater:
Abalone is a marine saltwater shellfish.
Mother of Pearl can be produced from both saltwater and freshwater shells.

Source:
Abalone's interior shell layer is made of mother of pearl.
Mother of Pearl is produced from pearl oysters, freshwater pearl mussels and abalone.

Edibility:
Abalone-flesh is considered a delicacy in some parts of the world.
Mother of pearl is not edible.