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| Formula | (Al,Mn3+,Fe3+)AlSiO5 |
| | Optic class & sign | Biaxial positive |
| | Optical orientation | a = X, b = Y, c = Z |
| | Optical plane | (010) |
| | Relief | Moderate-positive to high |
| | Refractive indices | nx = 1.650 -1.705
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ny = 1.654 -1.728
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nz = 1.662 -1.770
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| n increases with increasing Mn3+ and Fe3+ |
| | Birefringence (max.) | 0.012 - 0.065 |
| | | Δn increases with Mn3+ and Fe3+, anomalous interference colours; masking of interference colours by mineral colour |
| | Optic Angle
| 2Vx
|
| | 2Vz
= 59 - 85° |
| | Sign of elongation | Length-slow, l (+) |
| | Interference figure | As Mn (and Fe) increase, the simple first-order colour figure of andalusite changes to show increasingly higher-order isochrome rings in optic axis figures. In strongly coloured viridine, the superposition of the mineral colour on the interference colours is evident. |
| | Colour / pleochroism | Green to yellow pleochroic, absorption Y > Z > X, with X = light yellow to greenish yellow or yellowish green, Y = light to deep emerald green, Z = light to deep golden-yellow; colour distribution may be patchy; absorption increases with increasing Mn |
| | Zoning | |
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| Form | Habit | Granular, short columnar |
| | | Surface | Anhedral to euhedral |
| | Cleavage | 2 sets of {110} prismatic cleavage at nearly 90° |
| | Twinning | |
| | Extinction | Symmetrical to {110} prism faces and cleavage in sections ⊥ c; straight to prism faces and cleavage in sections parallel to c |
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| Reaction textures | |
| | Alteration / decomposition | Sericite, pyrophyllite, with Mn- or Fe oxides |
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| Occurence | Ign | |
| | | Met | Mn-Al-rich metapelitic and semipelitic rocks from oxidising environments |
| | | Sed | |
| | | Hyd | |
| | | Other | |
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| Distinctive properties | Green colour and characteristic pleochroism; mineral association |
| | Additional comments | In accordance with Deer, Howie & Zussman (1997), the name viridine is retained here. Viridine is optically quite distinct from common andalusite, while there is seemingly a continuous solid solution between the two minerals. The CNMNC-approved name for viridine is ferrian manganian andalusite (cf. Gunter & Bloss, 1982, Am. Mineral. 67, 1218-1228). Viridine with up to about 0.5 (Mn3++Fe3+) in octahedral position has been described. The name kanonaite is applied to compositions with Mn3+>Al in the M(1) position, and to the theoretical endmember composition Mn3+AlSiO5. Kanonaite from the type locality has a composition of Mn0.76Fe0.015Al0.23)AlSiO5. |
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