Homilite

Short description: Borosilicate mineral

Homilite

General
Category| Nesosilicate
Formula
(repeating unit)| Ca2(Fe2+,Mg)B2Si2O10
Strunz classification| 8/B.29-30
Crystal system| Monoclinic
Crystal class| Prismatic (2/m)
Space group| P21/b
Unit cell| a = 9.78 Å,
b = 7.61 Å,
c = 4.78 Å; β = 90.56°; Z = ?
Identification
Color| Greenish to brownish black
Mohs scale hardness| 5–​5 1⁄2
|re|er}}| Vitreous, resinous
Diaphaneity| Opaque
Specific gravity| 3.34
Optical properties| Biaxial (+)
Refractive index| nα = 1.715 nβ = 1.725 nγ = 1.738
Birefringence| δ =
2V angle| Measured: 80°
References| [1] [2] [3]

Homilite is a borosilicate mineral belonging to the gadolinite group of minerals with formula Ca
2(Fe,Mg)B
2Si

10.

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

1. ↑ Mineral Society of America Handbook (PDF)
2. ↑ Mindat with locations
3. ↑ Webmineral data
4. ↑ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine 85 (3): 291–320. doi:10.1180/mgm.2021.43. Bibcode: 2021MinM...85..291W.
5. ↑ 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.

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