Pure and homogeneous single crystals of orthorhombic mullite-type Bi 2 M 4 O 9 (M = Al 3+ , Ga 3+ , Fe 3+ ), and a mixed Bi 2 Fe 1.7 Ga 2.3 O 9 crystal from an equimolar Ga/Fe composition were grown by the top seeded solution growth (TSSG) method. All these compounds melt incongruently in the range of about 800 and 1100 °C. In case of bismuth gallate and ferrate inclusion-free crystals with dimensions up to several cubic centimeters can be grown. Limited solubility in Bi 2 O 3 and the high steepness of the liquidus curve are the reasons for getting only small imperfect bismuth aluminate crystals. In contrast to ceramic materials preparation reported in literature, divalent calcium and strontium could not be incorporated into the mullite-type structure during the melt growth process. Several fundamental physical properties like heat capacity, thermal expansion, heat conductivity, elastic constants, high-pressure behavior and oxygen diffusivity were determined by different research groups using single-crystalline samples from the as-grown materials. Furthermore, the refractive indices of Bi 2 Ga 4 O 9 were measured in the range of 0.430 and 0.700 μm. Such as many other bismuth containing compounds the refractive indices of Bi 2 Ga 4 O 9 are larger than 2, and Bi 2 Ga 4 O 9 is an optic biaxial positive crystal. Dedicated to Prof. Wolfgang Neumann on the occasion of his 65 th birthday