NACRE
Nacre is a usually whitish crystalline substance which oysters, mussels, snails, and other mollusks secrete around a foreign object (like a tiny stone) that has made its way into their shell. As layers of nacre coat the intruder, a pearl is formed over a period of many years.

NATURAL PEARL
A natural pearl (also called a genuine pearl) is a pearl that was produced in an oyster, freshwater mussel or other mollusk as a reaction to a tiny invading object that happened to be caught inside its shell.

NAVETTE
A navette is a gemstone which is cut as a marquise.

NICKEL SILVER
Nickel silver (also know as German silver) is an alloy consisting of mostly copper (roughly 60 percent), and approximately 20 percent nickel, about 20 percent zinc, and sometimes about 5 percent tin (then the alloy is called alpaca). There is no silver at all in German/nickle silver. This alloy was invented around 1860 in Germany as a silver substitute.

NOBLE METALS
The noble metals are gold, platinum, and silver. These are metals that are relatively impervious to chemical action.