Outstanding yellow orange acicular crystals of the extremely rare uranium mineral tristramite from the TL in Cornwall (Wheal Trewavas, Rinsey, Brea, Cornwall, United Kingdom). Ex Vandenbroucke Museum collection from Waregem, Belgium. — Photo: David Hospital · CC BY-SA 4.0
Tristramite
Tristramite is an IMA-recognized mineral species in the phosphate class, with the chemical formula (Ca,U⁴⁺,Fe³⁺)(PO₄,SO₄)·2H₂O.
It crystallizes in the hexagonal crystal system. It is a member of the Rhabdophane structural group.
Key properties: specific gravity 3.8–4.2; Vitreous luster; optically uniaxial.
IMA symbol Ttm, IMA status: approved, named in 1982.
Found in fractures and cavities in hydrothermal veins.
It is found associated with Uraninite, goethite, digenite, chalcopyrite, pyrite, sphalerite, galena, marcasite, quartz.
The name refers to Sir Tristram, a figure in the Arthurian legend.