Oriented transformation of linarite

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Abstract
The transformation of linarite into angiesite during thermal treatment has been studied by single-crystal x-ray diffraction methods. It was observed that a single crystal of linarite transformed into a single crystal of anglesite with randomly oriented tenorite crystals on it when linarite was heated to 400°C for 6 hours. Partial transformation of linarite into angiesite took place when the crystal was heated to 350°C for 6 hours. The orientational relationships between linarite and anglesite were as follows: a*lin‖[001]ang, [010]lin‖[010]ang, [001]lin‖[100]ang with 2alin ≈ 3cang, blin ≈ bang and 2clin ≈ aang. There seems to be another set of orientational relationships such as a*lin‖[[20(unk)]ang, [010]lin‖[010]ang and [001]lin‖[201]ang. The mechanism of transformation has been explained from a structural viewpoint. It has been suggested that the formation of angiesite from linarite took place by the removal from the linarite structure of Cu(OH)4 blocks, sandwiched between PbSO4 blocks, and closing up of the PbSO4 blocks to fill up the subsequent gaps. Slight orientations of the SO4 tetrahedra with respect to the Pb atoms were then necessary to form the anglesite structure.

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