Possible Clues:

• Brooch feature, maybe
• Valuable material in an area of land on far side of mountain
• Oyster part also called "mother-of-pearl"
• Mother-of-pearl from northern area
• Mosaic material
• Internal layer of a mollusk shell
• Pearly stuff
• Nautilus shell feature
• Pearl's mum seen in Northern area
• Shiny inner shell coating that makes pearls