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All refractory are based on fire clay, what it contains, alumina and silica. In fact all high heat resistant?firebricks?are made of fire clay. Like heat resistant mortars, insulation, pottery, ceramics, ceramic blankets or ceramic tiles on space shuttle, origins of these start from the fire clay, its melting starts at 1600 Celsius °C or 2912 Fahrenheit °F point. Only special manufacturing technologies of those expensive materials change their properties and usage applications. But we are not going to space, at least?not for now.