High‐temperature compression tests have revealed unsuspected high‐temperature strength in block talc. Analyses by x‐ray diffraction indicate that the increase in strength is associated with the transformation of the talc to protoenstatite, silica, and water. The bulk modulus of elasticity also increases with increasing temperature, reaches a maximum at 1100°C and then decreases at higher temperatures. These findings suggest that block talc is not as suitable for a solid pressure‐transmitting medium at elevated temperatures as is commonly supposed.

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