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| Formula | β-Ca2SiO4 |
| | Optic class & sign | Biaxial positive |
| | Optical orientation | X near c, Y near a, Z = b |
| | Optical plane | Orthogonal to (010) |
| | Relief | High |
| | Refractive indices | nx = 1.700 -1.715
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ny = 1.715 -1.723
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nz = 1.725 -1.740
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| | Birefringence (max.) | 0.023 - 0.025 |
| | | |
| | Optic Angle
| 2Vx
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| | 2Vz
= 60 - 73° |
| | Sign of elongation | Length-fast, l (-) |
| | Interference figure | |
| | Colour / pleochroism | Colourless |
| | Zoning | - |
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| Form | Habit | Granular, tabular |
| | | Surface | Subhedral to anhedral |
| | Cleavage | {100} |
| | Twinning | Lamellar on {100}, common |
| | Extinction | Symmetrical to {100} lamellar twins with X∧c = 13-14° in sections ⊥ Z; in sections ⊥ X straight extinction to {100} cleavage traces. |
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| Reaction textures | |
| | Alteration / decomposition | |
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| Occurence | Ign | |
| | | Met | Calcareous rocks in high-temperature contact metamorphic zones, also in pyrometamorphic environments |
| | | Sed | |
| | | Hyd | |
| | | Other | |
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| Distinctive properties | High relief, moderate Δn, lamellar twinning, restriction to high-T contact zones |
| | Additional comments | An alternative term ‘belite’ (or ‘C2S’ in cement chemistry) is used for larnite in the cement and refractory ceramics industry.
Bredigite, α-Ca2SiO4, is orthorhombic-pseudohexagonal, with similar relief, but low 2V (10-34°), and slightly lower Δn (0.013-0.019). Bredigite also occurs in high-T contact-metamorphic environments.
There is very little information in the literature on natural crystal habits of larnite. Hence, the crystal diagrams are purely schematic.
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