Nacre (L31) Flashcards
What is Mother of Pearl a common term for?
The lustrous, irdiescent material forming the inner surface of seashells
What is the Nacre?
The material comprising mother of pearl
What are the 3 invertebrate groups that Nacre production includes?
The Bivalves
Gastropods
Cephalopods
What are the 5 things that most molluscs possess?
A fleshy foot (used for locomotion)
A radula (rasping organ for feeding)
A digestive system with a stomach and gut
Gills
Mantle
What is the mantle?
a fleshy membrane of tissue that surounds the visceral mass.
in molluscs without an external shell, such as squids, the mantle is basically the skin
it also protects delicate internal tissues
AND most importantly it plays a role in shell secretion
What do the mantle secrete and then cover?
secretes prisms of calcium carbonate
then covers the layer with tablets of aragonite nacre
What happens when shell secretion is not taking place?
the mantle seperates from the shell, so seawater fills the gap in between
What is Periostracum?
an organic material deposited and provides protection from dissolution, and aids in camoflauge
Why do prismatic and nacreous layers have diff optical properties and what are they?
due to differences in crystal habit
the prismatic layer - weakly translucent to opaque
the nacreous layer - shiny, translucent and often colorful
Wht are Nacre largely composed of?
Largely, but not entirely, composed of aragonite crystals and films of organic matter and water
what are the tiny tablets of aragonite in nacre glued to adjacent tablets with?
Conchiolin represented by the dark lines
What are the 2 things that the quality of lustre in nacre is a function of?
First, the quality of surface reflection (determines the brilliance of the lustre)
second, the quality of internal reflection also influences lustre
What is Orient?
The iridescent play of colors in nacre
what is one contribution to orient?
the splitting of light waves (diffraction) into individual colors at the spectrum due to the regular arrangement of grooves and ridges on a surface
What happens when individual crystals of aragonite act as tiny prisms?
refracts light and disperses it into the colours of the rainbow
What is thin firm interference?
the incoming light waves and the reflected light waves constructively interfere in such a way as to produce diff interference colors at diff angles of viewing
What is a popular aesthetic practice?
to remove teh outer prismatic layer of a shell to reveal the mroe attractive, shiny, nacreous layer underneath
What is Nautilus?
one of the most famous photographs ever made
What is a gemostone that has recently entered the gemstone market?
Ammolit
Why is Ammolite, Fossil ammonite nacre rare?
b/c under normal preservational circumstances, aragonite either dissolves or is recrystallized to the more stable form of calcium carbonate, calcite
Why is the Bearpaw Shale greatly enhanced in intensity of color?
the bold colors are produced due to loss of organic layers between the sheets of aragonite which otherwise limit the transmission of light through nacre and cause the milker appearance of mother of pearl in unfossilized modern molluscs
Why is ammolite so hard to work with?
it readily splits apart along planes between aragonite sheets and is quite soft and prone to scratching
Most ammolite is mounted in ____ form
Triplet
How will you typically see ammoite in a jewellery store?
as a ammolite triplet cabochon
