Some Effects of Artificial Heating on Fluorite-Bearing Albite-Granite from St. Austell, Cornwall

The granite consisted chiefly of albite, quartz, muscovite, microperthite, fluorite, and topaz; zircon was very rare. The low to high quartz transition enhanced thermal expansion and porosity. Heating was continued step-wise to 1,300°C. and caused an irreversible increase in porosity at all temperatures investigated. The changes undergone by the various minerals, separately or through interaction, were noted. Fluorite began to melt against muscovite or alkali-feldspar between 800° and 900°C. Muscovite developed brownish pleochroism at the lower, and was replaced by mullite at the higher, temperatures. The gradual melting of feldspar, the development of cleavages and cracks in quartz, and the invasion of these cracks by feldspathic glass resembled phenomena in certain xenoliths.The conditions that produced glass when powdered granite was heated unconfined or in a bomb are described.