Absorption of light by exchange coupled pairs of tetrahedrally coordinated divalent manganese in the helvite-genthelvite solid solution

作者：Halenius Ulf^*

来源：Periodico di Mineralogia, 2011, 80(1): 105-111.

DOI：10.2451/2011PM0008

• helvite
• genthelvite
• electronic spectroscopy
• electron microprobe analyses

Intensified colours in the helvite-genthelvite solid solution series are demonstrated by means of single crystal optical absorption and electron microprobe techniques to be due to absorption of light by exchange coupled (IV)Mn(2+)-(IV)Mn(2+) pairs. The absorption bands caused by the pair transitions occur at energies, 21100, 22600, 23800, 26800 and 28400 cm(-1), that are comparable to those recorded for spin-forbidden single ion transitions in (IV)Mn(2+), but the absorption coefficients of the bands are proportional to the square of the Mn-contents of the samples instead of simply showing a Lambert-Beer relationship to the Mn-content. The helvite structure, comprising four corner sharing MnO(3)S tetrahedra with a common sulphur anion apex, represents a favourable situation for formation of exchange coupled 3d-cation pairs. However, several common Mn-rich minerals, as, e.g., rhodonite, have comparably favourable structures that contain corner, edge or face sharing 3d-cation centred polyhedra. Consequently, may Mn(2+)-Mn(2+) pair absorption be a frequent cause for colour intensification in minerals.

• 出版日期2011-4