Crystallization of BeO, Be2SiO4, and SiO2 from Li2MoO4--MoO3

Single crystals of phenacite (Be 2 SiO 4 ), bromellite (BeO), and tridymite (SiO 2 ) were grown from an Li 2 MoO 4 ‐MoO 3 flux. Phenacite, with rhombohedral symmetry, grew in three distinct shapes with aspect ratios (length/width) as follows: needles (>3), rods (>1.1 to 1.5), and rhombohedral‐faced crystals (=1). The latter grew as single crystals; the others were twinned on the . For most experiments the temperature was held constant at 1165°C and the Li 2 MoO 4 /MoO 3 ratio at 1/16. The growth mechanism for crystallization was the evaporation of MoO 3 . The system produced one to three phases, depending on the BeO/SiO 2 ratio. Bromellite grew until a BeO/SiO 2 ratio of 0.8 was attained. It grew as a hemipyramidal crystal having a short prism with a curved top or as a hexagonal plate. The pyramid‐ and prism‐shaped crystals were twinned, although a few hexagonal plates were single. Tridymite grew in small hexagonal plates when the BeO/SiO 2 ratio was less than 1.5. The effect of temperature, nucleation, and flux composition on crystal shape, twinning, and occurrence is discussed.