Heat stones were similar in appearance to the crystalline lightstones, but produced less light, and much more heat - enough, in fact, to instantly melt ice. To contain this heat and make it safe to hold, the actual stone itself was contained inside a handheld, heat-retentive metal canister resembling a miniature version of those which had held the Toa Mata, albeit with four holes in the domed cap instead of six. This lid could be easily removed to access the heat stone's warmth, and was kept shut when not in use.