Pearls
Many different kinds of molluscs can produce pearls. Pearls from the queen conch, S. gigas, are rare and have been collectors' items since Victorian times. Conch pearls occur in a range of hues, including white, brown and orange, with many intermediate shades, but pink is the colour most associated with the conch pearl, such that these pearls are sometimes referred to simply as "pink pearls". In some gemological texts, non-nacreous gastropod pearls used to be referred to as "calcareous concretions" because they were "porcellaneous" (shiny and ceramic-like in appearance), rather than "nacreous" (with a pearly lustre), sometimes known as "orient". The GIA and CIBJO now simply use the term "pearl" — or, where appropriate, the more descriptive term "non-nacreous pearl" — when referring to such items, and under Federal Trade Commission rules, various mollusc pearls may be referred to as "pearls" without qualification.
Although non-nacreous, the surface of fine conch pearls has a unique and attractive appearance of its own. The microstructure of conch pearls comprises partly aligned bundles of microcrystalline fibres that create a shimmering, slightly iridescent effect known as "flame structure". The effect is a form of chatoyancy, caused by the interaction of light rays with the microcrystals in the pearl's surface, and it somewhat resembles Moiré silk.
Read more about this topic: Conch
Famous quotes containing the word pearls:
“Instead of pearls a wrought clasp
a bracelet will you accept this?”
—Hilda Doolittle (1886–1961)
“When I was one-and-twenty
I heard a wise man say,
“Give crowns and pounds and guineas
But not your heart away;
Give pearls away and rubies,
But keep your fancy free.”
But I was one-and-twenty,
No use to talk to me.”
—A.E. (Alfred Edward)
“Or else I thought her supernatural;
As though a sterner eye looked through her eye
On this foul world in its decline and fall,
On gangling stocks grown great, great stocks run dry,
Ancestral pearls all pitched into a sty,
Heroic reverie mocked by clown and knave....”
—William Butler Yeats (1865–1939)