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Science  12 Jun 2009:
Vol. 324, Issue 5933, pp. 1407
DOI: 10.1126/science.1173605

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Herapathite crystals were first prepared when an assistant to the toxicologist Herapath mixed iodine with the urine of a quinine-fed dog. Herapath was shocked when his transparent crystals sitting one atop the other at right angles were “black as midnight” and predicted that they would replace costly mineral polarizers. Such a change in practice in optics had to await Land, who oriented fragile herapathite microcrystals in extruded polymers, a process that produced the first large-aperture light polarizers and, in turn, the Polaroid empire. Curiously, the crystal structure of herapathite has never been established, and thus its chromophore and mechanism of action remain a mystery. The single crystal structure of herapathite is herein established, and its complete dichroism can be attributed to delocalized excitations along …I3-…I3-… chains. The workings of herapathite, one of the most successful serendipitously engineered crystals, is only now understood.

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