Potassic-magnesio-fluoro-arfvedsonite

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Potassic-magnesio-fluoro-arfvedsonite is a rare amphibole mineral first found in Quebec, Canada, in very old rocks of the Canadian Shield. The rocks hosting it date from the Archean to the Proterozoic eon, roughly 2.5 billion to 538 million years ago.

Properties
- Color: bluish-gray; luster: vitreous; streak: white
- Hardness: 6 on the Mohs scale; specific gravity: 3.174 g/cm3
- Cleavage: perfect on {110}; fracture: splintery
- Crystal system: monoclinic; space group: C2/m
- Crystal structure: double-chain inosilicate
- Optical: biaxial negative
- Twinning: common, especially on {100}

Chemistry and naming
- Formula: (K,Na) [Na2] [Mg4Fe3+] [Si8O22] [(F,OH)2]
- IMA symbol: Pmfarf
- It is an arfvedsonite that contains magnesium, potassium, and fluorine
- History: discovered in 1985 in Quebec; naming has changed over time, with the current name adopted in 2012

Occurrence and geology
- Regions where it has been found: Quebec (Canada), Montepuez (Mozambique), Troms og Finnmark (Norway), Dakhla-Oued Ed-Dahab (Morocco), Las Vegas (USA)
- Associated rocks: occur in complex mafic ultrapotassic peralkaline igneous rocks with high silica, often alongside lamproite
- Rock ages in these locations range from late Archean to Proterozoic

Additional notes
- X-ray diffraction and related measurements yield monoclinic cell parameters and a unit cell that support its classification as a monoclinic, double-chain inosilicate amphibole.