Polymorphous

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

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

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

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

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