Alpha/ Beta phase of Nickel Sulphide

Spontaneous breakage of tempered glass may be due to the Nickel Sulphide inclusion changing from a high temperature phase( alpha) to a low temperature phase(beta).

Is there a temperature range defining the alpha phase and beta phase? I think 600 degC can probably achieve alpha phase and 290 degC can already achieve beta phase? How do u think?

many thx

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