The preservation of quartz grain surface textures following vehicle fire and their use in forensic enquiry

During a terrorist trial, dispute arose as to whether the temperature produced in a car fire was sufficient to destroy quartz grain surface textures. A series of seven sequential experiments showed that the temperature for quartz surface texture modification/destruction and the production of vugs, vesicles and glassy precipitation (‘snowdrifting’) occurred at 1200 °C under normal atmospheric conditions. By adding a number of man-made and natural substances, it was found that only the presence of salts depressed this modification temperature (to 900 °C). Experiments to determine the temperature of fire in a car indicated that the maximum temperature produced under natural conditions (810 °C) was insufficient to affect the quartz grain surface textures. These results confirm the use of surface texture analysis of quartz grains recovered from the remains of cars subjected to fire and their use as a forensic indicator.