Assertion: sponge's skeleton | /r/MadeOf | calcite
Facets:
Source sentences:
text: Calcarea - These have skeletons made of Calcite.
text: Calcarea have skeletons made of calcite, a form of calcium carbonate, which may form separate spicules or large masses.
text: They are sponges with a soft body that covers a hard, often massive skeleton made of calcium carbonate, either aragonite or calcite.