Morphologies and mechanical properties of basalt fibre processed at elevated temperature

•Morphologies and properties of basalt fibre processed at different temperatures were studied.•Reduction on the strength of fibre upon thermal treatment occurred in three steps.•Thermal treatment led to the formation of crystal on fibre surface.•Crystallization on fibre began with the spontaneous formation of spinel phase.•Spinel crystal was the nucleation site for the formation of pyroxene structure.