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Dimorphous and Polymorphous Minerals

Dimorphous means that two minerals have the same basic chemistry, but have different crystal structures. And of course, Polymorphous is when three or more minerals have the same basic chemistry but have different structures.

A good example of trimorphism is Andalusite, Kyanite and Sillimanite (Fibrolite). All three have the same basic chemistry, Al₂SiO₅, but Andalusite is Orthorhombic, Kyanite is Triclinic and Sillimanite is Orthorhombic.

Dimorphous Minerals

Anorthite (triclinic) :: Svyatoslavite (orthorhombic)

Boracite (orthorhombic) :: Trembathite (trigonal)

Catapleiite  (monoclinic) :: Gaidonnayite (orthorhombic)

Cavansite (orthorhombic) :: Pentagonite (orthorhombic)

Cordierite (orthorhombic) :: Indialite (hexagonal)

Cubanite (orthorhombic) :: Isocubanite (isometric)

Natrolite (orthorhombic) :: Gonnardite (orthorhombic)

Phosphosiderite (monoclinic) :: Strengite (orthorhombic)

Pyroxmangite (triclinic) :: Rhodonite (triclinic)

Kurnakovite (monoclinic) :: Inderite (triclinic)

Lepidocrocite (orthorhombic) :: Goethite (orthorhombic)

Zircon (tetragonal) :: Reidite (tetragonal)

Zoisite (orthorhombic) :: Clinozoisite (monoclinic)

Polymorphous Minerals

Anatase (tetragonal) :: Brookite (orthorhombic) :: Rutile (tetragonal)

Andalusite (orthorhombic) :: Kyanite (triclinic) :: Sillimanite (orthorhombic)

Aragonite (orthorhombic) :: Calcite (trigonal) :: Vaterite (hexagonal)

Diamond (isometric) :: Chaoite (hexagonal) :: Graphite (hexagonal) :: Lonsdaleite (hexagonal)

Forsterite (orthorhombic) :: Ringwoodite (isometric) :: Wadsleyite (orthorhombic)