Frondelite , Phosphosiderite Locality: Buranga pegmatite, Gatumba District, Western Province, Rwanda Size: 4.4 cm x 2.4 cm x 0.4 cm Frondelite and phosphosiderite are rare phosphates and this is an extremely rare combination from this very obscure and unusual, Al-rich phosphate pegmatite. Brown crusts of frondelite and patches of violet phosphosiderite are scattered on both sides of the sliver of matrix. Metastrengite is a synonym of phosphosiderite. Probably material from the 1950s to 1980s. Ex. Gilbert Gauthier and Jacques Montandon Collections. — Photo: Robert M. Lavinsky · CC BY-SA 3.0
Frondelite
Frondelite is an IMA-recognized mineral species in the phosphate class, with the chemical formula (Mn²⁺₀.₅Fe³⁺₀.₅)₂Fe³⁺₃(PO₄)₃(OH)₅.
It crystallizes in the orthorhombic crystal system (space group Cmcm). It is a member of the Rockbridgeite structural group.
Key properties: Mohs hardness 4.5; specific gravity 3.453; Vitreous to dull luster; optically biaxial.
IMA symbol Fnd, grandfathered status — known before the IMA’s founding, named in 1949.
An alteration product of primary phosphates in complex granite pegmatites.
It is found associated with Triphylite, vivianite, heterosite–purpurite, cyrilovite, phosphosiderite, leucophosphite (Sapucaia mine, Brazil).
The mineral was named to honor Dr. Clifford Frondel (1907–2002), American mineralogist, Professor of Mineralogy, Harvard University, Cambridge, Massachusetts, USA.