Homilite

Borosilicate mineral

5+1⁄2LusterVitreous, resinousDiaphaneityOpaqueSpecific gravity3.34Optical propertiesBiaxial (+)Refractive indexn_α = 1.715 n_β = 1.725 n_γ = 1.738Birefringenceδ =2V angleMeasured: 80°References^[2] ^[3] ^[4]

Homilite is a borosilicate mineral belonging to the gadolinite group of minerals with formula Ca₂(Fe,Mg)B₂Si₂O₁₀.

It occurs as brown monoclinic crystals (space group P2₁/a^[5]) within feldspar masses in pegmatite and was discovered in 1876 in Stoko island, Langesundfiord, Norway. The name is from the Greek for to occur together, in allusion to its association with meliphanite and allanite.

References

^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
^ Mineral Society of America Handbook (PDF)
^ Mindat with locations
^ Webmineral data
^ Miyawaki, R.; Nakai, I.; Nagashima, K. (15 January 1985). "Structure of homilite, Ca2.00(Fe0.90Mn0.03)B2.00Si2.00O9.86(OH)0.14". Acta Crystallographica Section C Crystal Structure Communications. 41 (1): 13–15. doi:10.1107/S010827018500261X.