DAVID VEBLEN'S DISCOVERY OF NON-CLASSICAL BIOPYRIBOLES

David Veblen arrived at Harvard in the fall of 1965. Upon my arrival in 1966, I learned he was already expressing interest in studying mineralogy. As a junior he was the only undergraduate in my crystal symmetry and X-ray diffraction course. Senior year he asked if he could do his honors thesis in structure analysis. That study comprised refinements of synthetic hedenbergite and an Fe-rich diopside. which constituted his first scientific paper, delivered after his 1969 graduation at a GAC-MAC meeting in Montreal.

David returned to Harvard for graduate work in the fall of 1973, more than ready to resume his study of structural mineralogy. In conversations with Jim Thompson, who at the time was skeptical of the reported space group of orthorhombic amphiboles, David was directed to what Jim thought would be an excellent locality to find pure anthophyllite: the Carleton talc mine in Chester, Vermont. Much to his – and my – surprise, the first precession photographs of a single crystal from that quarry showed it was clearly not amphibole. Mindful of Jim Thompson’s elegant description of the structure of amphibole as an alternation of (010) slabs of pyroxene (P) and mica (M), and his speculation that slab sequences more complex than amphibole (MP) double chains might exist, David realized that his photographs could best be interpreted as diffraction from such an unrecognized sequence. Unit-cell dimensions of the first crystal analyzed suggested the structure could be made up of (010) slabs containing an ordered (MMPMP) sequence of combined triple and double chains. Other single crystals displayed diffraction patterns consistent with an ordered sequence of triple silicate chains (MMP).

Thus were discovered the first non-traditional biopyriboles: the orthorhombic triple-chain (MMP) jimthompsonite and the first mixed-chain (MMPMP) biopyribole chesterite and their monoclinic polymorphs. David solved and refined the structures of the new biopyriboles simply by constructing models, based on the Thompson slab hypothesis, that satisfied the observed unit cells and space groups. David’s Ph.D. thesis (1976) reported these discoveries.

David moved on from Harvard to a post-doctoral position at Arizona State University, where he examined the microstructures of non-classical biopyriboles with Peter Buseck using HRTEM techniques.