Q 01/05

Inside which part of a mollusc does a pearl form?

A) The gill

B) The foot

C) The hinge

D) The mantle

Answer · why

D) The mantle

The mantle is the soft tissue that also secretes the shell, and it coats any intruder in layer after layer of nacre.

Q 02/05

Pearls are made mainly of which mineral?

A) Silicon dioxide

B) Calcium phosphate

C) Calcium carbonate

D) Magnesium oxide

Answer · why

C) Calcium carbonate

It is deposited as aragonite, or a mix of aragonite and calcite, in concentric layers, just like the shell itself.

Q 03/05

What is the name for the substance, also called mother-of-pearl, that pearls are built from?

A) Nacre

B) Keratin

C) Chitin

D) Enamel

Answer · why

A) Nacre

It is a combination of aragonite platelets and the horn-like protein conchiolin.

Q 04/05

Why does nacre appear iridescent?

A) It contains dissolved traces of copper and iron

B) It absorbs ultraviolet light and re-emits it as colour

C) Its aragonite platelets are about as thick as a light wavelength

D) Its surface is coated in a thin oil secreted by the mollusc

Answer · why

C) Its aragonite platelets are about as thick as a light wavelength

The layers reflect, refract and diffract light; the thinner and more numerous they are, the finer the lustre.

Q 05/05

The popular belief that pearls start around a grain of sand is described as what?

A) True for saltwater pearls only

B) Rarely the case

C) Proven by X-ray studies

D) Universal for natural pearls

Answer · why

B) Rarely the case

Parasites, organic debris or displaced mantle tissue are the usual triggers.