Complex sentence: Flakes a millimetre or two thick can be bent between the fingers and are said to give out a creaking sound, but specimens showing this property form only a small part of the whole mass of the rock.
Split into simpler sentences: Flakes a millimetre or two thick can be bent between the fingers and are said to give out a creaking sound. It should be noted that specimens showing this property form only a small part of the whole mass of the rock.