We manufacture Zircon Flour. The specs are as follows.

SIZE 300 MESH TO 320 MESH (POWDER).
40 TO 80 (GRITS SIZE).
SOFTENS 1450 TO 15000 C
SHRINKAGE 1600 TO 17000 C
MELTING 1900 TO 20000 C
HARDNESS 7 TO 7.5%
BULK DENSITY
1.60(FOR POWDER)
COLOUR WHITE
ZrO2. 62 TO 65%
SiO2 30 TO 35%
TiO2 0.13%
Fe2O3 0.11%
Al2O3 0.16%
CaO 0.04%
MgO 0.01%
PeO5 0.01%

Kindly let's know if it suits your requirement.

Also available Muscovite Mica Powder stable upto 1100 C. It's being used by leading friction products and high-temperature grease manufacturers.