What are seashells made of?

Answer 1

Seashells are, quite simply, the exoskeletons of mollusks.The blood of a mollusk is rich in a liquid form of calcium. A soft, outer organ called the mantle concentrates the calcium in areas where it can separate out from the blood, forming calcium carbonate crystals. The mantle deposits sheets of the crystal in varying thicknesses. The individual crystals in each layer vary in shape and orientation.
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Answer 2

A shell may be made of nacre (a combination of calcium and protein), chitin, bone and cartilage, or silica.

While many sea animals produce exoskeletons, usually only those of molluscs (also spelt "mollusk") are normally considered to be "sea shells". The majority of shell-forming molluscs belong to the classes Gastropoda (univalves, or snails) or Bivalvia. Three other shell-bearing classes are Scaphopoda (tusk shells), Polyplacophora (segmented chitons) and Monoplacophora (single-shelled chiton-like animals, also called Tryblidia). Some species of Cephalopoda also build shells, including the primitive Nautilus order which produces the famous "chambered Nautilus" shell; although some taxa of cephalopods such as octopuses and squid only form small internal shells.

The majority of shells are made of nacre, an organic mixture of outer layers of horny conchiolin (a scleroprotein), followed by an intermediate layer of calcium carbonate (CaCO3) as either calcite or aragonite in the form of platy crystals. Shells of the class Polyplacophora are made of a softer calcium carbonate compound called chiton.

Nacre is secreted by the epithelial cells (formed by the germ layer ectoderm) of the mantle tissue of certain species of mollusk. Mollusk blood is rich in dissolved calcium. In these mollusks the calcium is concentrated out from the blood where it can crystallize as calcium carbonate. The individual crystals of each layer differ in shape and orientation. Nacre is continually deposited onto the inner surface of the animal's shell (the iridescent nacreous layer also known as mother of pearl), both as a means to smooth the shell itself and as a defense against parasitic organisms and damaging detritus.

Answer 3

A shell is the hard, rigid outer covering, or integument, of certain animals. More specific scientific names include exoskeleton, carapace, and peltidium. A shell may be made of nacre (a combination of calcium and protein), chitin, bone and cartilage, or silica.

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Answer 4

Calcium carbonate largely. One would assume there is a protein matrix holding it together as well

Answer 5

calcium carbonate