Experimental Frost Shattering of Some Precambrian Rocks, Finland

Abstract

The intensity of frost shattering and the amount and type of debris produced from quartzite, granulite and rapakivi granite samples were studied with laboratory experiments. The experiments were run for 1103 temperature cycles from + 15°C to -8°C. The amounts of debris ranged from 0.01 to 0.8 percentages of debris relative to dry weight of the original samples. Grain size of frost weathered material was mainly in sand and gravel fraction classes. Surface texture of quartz grains was studied with SEM. Shape of the grains was irregular and their edges were sharp. Many of the surfaces were rather smooth. Irregular conchoidal fractures are also characteristic. Very often the surfaces were covered by very small, flat fragments of quartz. Some opened microfissures were also found in the grains. The Finnish rocks seem to be very resistant to frost weathering and postglacial frost shattering has had rather limited importance in landform formation in Finland.