Three kinds of MgGeO 3 pyroxene single crystals of 1-10 mm size were grown by the flux method: an orthopyroxene, a clinopyroxene, and a "clino-from proto" phase. The lattice parameters and the space groups are (1) orthopyroxene: a = 18.8099(12), b = 8.9484(8), c = 5.3451(4)Aa, Pbca, (2) clinopyroxene and (3) "clino-from proto" phase: a = 9.6010(8), b = 8.9323(6), c = 5.1592(5)Aa, beta = 101.034(9) degrees , C2/c. The phase relations of MgGeO 3 were studied in the temperature range 655-1030 degrees C and in the pressure range 0-55 kbar. The boundary between orthopyroxene and clinopyroxene was determined as T = 810 degrees C + 3.8 P(kbar), where the high-pressure and low-temperature phase is monoclinic. Single crystals of ilmenite-type MgGeO 3 (up to 100 mu M in size) were also grown in association with the pyroxene-->ilmenite transformation at 55 kbar, using the flux-grown orthopyroxene or clinopyroxene MgGeO 3 single crystals as starting materials.--Modified journal abstract.

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