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Silicon powder in a reaction-sintered silicon nitride crucible was heated at 1600℃ in a nitrogen atomosphere. Clustered β-Si_3N_4 single crystals were obtained in residual silicon metal after cooling. The silicon residuals were dissolved by chemical purification using a mixture of aqueous HF and HNO_3, and subsequently treated and with H_2SO_4. Scanning electron microscopy observation showed that large β-Si_3N_4 crystals without Si residuals could be successfully separated by this process.