White crystal aggregates of the very rare silicoborate mineral harkerite from the TL in the small island of Skye, Scotland (Camas Malag, Torrin, Isle of Skye, Scotland, United Kingdom). Ex Vandenbroucke Museum collection from Waregem, Belgium. — Photo: David Hospital · CC BY 4.0
Harkerite
Harkerite is an IMA-recognized mineral species in the silicate class, with the chemical formula Ca₄₈Mg₁₆[AlSi₄O₁₅(OH)]₄(BO₃)₁₆(CO₃)₁₆·2(H₂O,HCl).
It crystallizes in the hexagonal crystal system (space group R-3m). It is a member of the Harkerite structural group.
Key properties: specific gravity 2.95–2.96; Vitreous luster.
IMA symbol Hkr, IMA status: approved, named in 1951.
Found in skarns in dolomitic limestones at the contact with granite (Camas Malag, Scotland); in volcanic ejecta (Alban Hills, Italy).
It is found associated with Calcite, monticellite, diopside, magnetite, vesuvianite, cuspidine, phlogopite.
The name refers to Alfred Harker (1859–1939), British petrologist, Cambridge University, Cambridge, England.