Assertion: iron | /r/HasProperty | found of greatest importance
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Source sentences:
text: Iron is also found combined with other elements in hundreds of minerals; of greatest importance as iron ore are hematite (ferric oxide, Fe 2 O 3 ), magnetite (triiron tetroxide, Fe 3 O 4 ), limonite (hydrated ferric oxide hydroxide, FeO(OH)∙nH 2 O), and siderite (ferrous carbonate, FeCO 3 ).