FASSAITE
FASSAITE “Fassaite” – (Ca,Na)(Mg,Fe2+,Al,Fe3+,Ti)[(Si,Al)2O6] – is a discredited term referring to a variety of augite characterized by high Fe³⁺ and Al contents and low Na content. The name originates from the Fassa Valley, in the Province of Trento, Italy. Another term used for the same material is “pyrogom.” There is a contradiction in the published […]
FREIESLEBENITE
FREIESLEBENITE Freieslebenite – AgPbSbS3 – is a very rare sulfosalt, characteristic of Pb-Ag-Sb-Bi parageneses. It is a minor silver ore, containing 20.24% Ag, 22.84% Sb, and 38.87% Pb. It is classified within the Freieslebenite Group, alongside marrite (containing As instead of Sb), and is one of several sulfosalts of similar composition. Chemically, it resembles diaphorite. […]
FERGUSONITE
FERGUSONITE “Fergusonite” – general formula (Y, ETR) NbO4 – is a term referring to several different, relatively common minerals. They are oxides classified into two groups and serve as very important ores for strategic elements. They are complex oxides with the general formula ABO₄, containing Y in solid solution with Rare Earth Elements (REEs), Nb, […]
FRANKLINITE
FRANKLINITE Franklinite – Zn2+Fe3+2O4 – is a very rare oxide. It is, or was, abundant in only a few locations. In the Franklin Mining District (New Jersey, USA), it was an important ore of Zn and Mn. The deposit has been depleted for decades, and today the mines are open to visitors; famous for the spectacular […]
FIBROLITE
FIBROLITE See “Sillimanite”.
FROODITE
FROODITE Froodite – α-PdBi2 – is a very rare sulfide (an alloy of metalloids with Platinum Group Elements), of no importance as an ore. It may contain Te. 1. Characteristics Crystal system: Monoclinic prismatic. Color: Gray. Highly reflective in silvery white. Tarnishes quickly. Habit: Rounded grains. Cleavage: {100} perfect, {001} distinct. Tenacity: Brittle Twinning: Sometimes. […]
FORSTERITE
FORSTERITE Introduction See “Olivine”
FAYALITE
FAYALITE See “Olivine”.
FAHLORE
FAHLORE See “Tetrahedrite-Tennantite” “Fahlore” is derived from the German “Fahlerz” (“pale ore”, an ore with “faded” colors) and the English suffix “-ore”. “Fahlore” is used since 1805.
FERBERITE
FERBERITE See “Wolframite”