• A relatively rare blue mineral, (Mg, Fe)Al<sub>2</sub>(PO<sub>4</sub>)<sub>2</sub>(OH)<sub>2</sub>, with a vitreous luster.
  • A mineral of a light- or indigo-blue color, crystallizing in the monoclinic system.
  • A mineral of a light indigo-blue color, occurring in small masses, or in monoclinic crystals; blue spar. It is a hydrous phosphate of alumina and magnesia.
  • A semi-precious <xref>gemstone</xref> that is a basic <xref>phosphate</xref> of <xref>magnesium</xref>, <xref>iron</xref> and <xref>aluminium</xref>
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